“MICE TRAP” 1

Running head: “MICE TRAP” AND THE MENTAL LEXICON

What “Mice Trap” Tells us about the Mental Lexicon

Carolyn J. Buck-Gengler1,3, Lise Menn2,3, and Alice F. Healy1,3

University of Colorado at Boulder

1Department of Psychology 2Department of Linguistics

3Institute of Cognitive Science

Address correspondence to:

Dr. Carolyn Buck-Gengler

Department of Psychology

345 UCB

University of Colorado at Boulder

Boulder, CO 80309-0345 USA

Phone: 303.492.4156

FAX: 303.492.8895

Email: Carolyn.Buck-Gengler@Colorado.edu

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Abstract

Processing difficulty can account for the greater acceptability of irregular than regular

plurals in English compounds. Experiments 1 and 2 involved English noun-noun compound

production. Experiments 3 (English) and 4 (miniature artificial language) involved production of

either singular or plural forms from the same or opposite form. More irregular than regular

plurals were used in compounds, and it took longer to produce irregular than regular singulars

from plurals. Responses were faster when cue and required response number matched than when

they differed in both English and the artificial language. Differences between regular and

irregular plurals in compounds are, thus, explainable by processing factors, without appealing to

innate grammar.

Keywords: Inflectional Morphology, Regular and Irregular Noun Plurals, Noun-noun

Compounds

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What “Mice Trap” Tells us about the Mental Lexicon

Inflectional morphology is a frequently used test-bed for examining theories and models

of the mental lexicon. The issue of regularity within inflectional morphology has been an

especially important area of research and debate about the nature of language representation and

even the innateness of language. A central aspect of this debate concerns whether the linguistic

description involving a strict separation between rules and memory is supported experimentally.

Instead, experimental results and psycholinguistic and computational models might point to

alternative constructions of the lexicon.

The present study reexamines one of the early experiments reported in this debate,

involving regular and irregular English noun morphology. That experiment (Gordon, 1985) has

been cited often as support for dual mechanism models (rules for regulars and rote memory or an

associative network for irregulars), innateness, and level ordering of morphology (Kiparsky,

1982a). In the experiments presented here, we examine the possibility of a simple alternative

processing explanation for the earlier reported results.

The regular/irregular distinction for English noun morphology can be summarized as

follows. Most nouns take the regular orthographic -s plural, phonologically /-s, -z, -Iz/. However,

a number of nouns do not fit that pattern. Mass/non-count nouns have no plural form and are

irrelevant to the morphological discussion (e.g., corn). Irregular nouns include nouns with zero

plural (e.g., sheep), nouns of foreign origin that use the foreign plural (e.g., stimulus/stimuli,

analysis/analyses, datum/data), and a small number of nouns that have synchronically

idiosyncratic plurals based on earlier systematic changes that have been lost over time (e.g.,

mouse/mice, foot/feet). Semi-regular nouns (mostly ending in /f/) add the -s but change the final

consonant voicing (e.g., life/lives, loaf/loaves); because they are semi-regular they were not used

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in the present study.

Regularity/irregularity has consequences extending beyond the choice of inflected form,

for instance, noun-noun compound formation in English. In general, the first noun of a noun-

noun compound must be singular, but plurals of irregular nouns are more acceptable in that

position (e.g., Gordon, 1985; Kiparsky, 1982a, 1982b; Pinker, 1994, 1999). So, even when

talking about more than one rat or toy, one would not say *rats catcher or *toys box. However,

mice catcher is far more acceptable. This dichotomy can be explained within the theory of level

ordering of morphology (Kaisse & Shaw, 1985; Kiparsky, 1982a, 1983), although that theory has

been shown to have serious limitations (Bauer, 1990; Fabb, 1988; Haskell, MacDonald, &

Seidenberg, in press; Ramscar, 2002).

In level ordering, assembly of words proceeds at several “levels.” At Level 1, a base form

(for almost all English nouns, the singular) or another memorized form (such as the irregular

plural) is retrieved from the mental lexicon. Unproductive derivations, especially those that

impose phonological or stress changes in the stem, are also found here. At Level 2, compounds

are formed (productive derivational affixes, such as un-, -less, and -ly, are also added here). At

Level 3, after compound formation, regular affixes such as the regular plural are added. The

normative English pattern dispreferring *rats trap is explained by saying that the regular plural

rats is created too late (at Level 3) to be placed inside a compound (at Level 2). However,

irregular plurals, being retrieved from memory at Level 1, are easily incorporated during

compound formation, and thus should be optionally allowed. Problems with exceptions to the

rule (e.g., civil rights commission, public works department, etc.) have been explained by appeals

to various factors that permit exceptions (Kiparsky, 1982a; Pinker, 1999).

Gordon (1985) and Children’s Compound Formation

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Gordon (1985) explored compound formation in a language production experiment with

children aged 3-5. The children were introduced to a puppet with a voracious appetite (Cookie

Monster). Various objects that Cookie Monster might eat were shown to each child. Each time

the child first named the object, then was asked, “What do you call someone who eats X?” The

children were trained to answer with a noun-noun compound in the form of X-eater. For each

test noun, the singular and plural of the noun were elicited in turn by showing the child first one

and then several of the object represented by the noun, and asking the child to name what he or

she saw. Whichever form of plural a child gave (e.g., for the plural of mouse: mice, mouses,

mices) was used in the compound elicitation. The main test words were five irregular nouns (i.e.,

mice, teeth, geese, men, and feet) semantically matched with five regular nouns (i.e., rats, beads,

ducks, babies, and hands).

Gordon (1985) found that for regular nouns (and for irregular nouns which were

overregularized, e.g., mouses), close to 100% of the compounds were formed with the singular

form for X in X-eater (e.g., rat-eater). On the other hand, 90% of the irregular nouns for which a

child produced the correct irregular plural received irregular plural responses (e.g., mice-eater).

In other words, if the plural was “regular” (whether correct or not), the singular was produced,

whereas if the plural was irregular, the plural was (almost always) produced. Thus the results

matched the predictions of level ordering well. Gordon attributed the extremely high rate of

plural response for irregulars (90% rather than the random 50% rate that the theoretical

“optional” choice of the plural first element suggests) to the fact that the experiment was set up

to bias for plural in all cases.

Gordon (1985) claimed that these results were strong support for the innateness of the

underlying grammar (level ordering), because he also asserted, based on an examination of

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compounds found in the Kuc&era and Francis (1967) word list, that children only rarely hear

irregular plurals in compounds. Thus children would not have the opportunity to learn that

irregular plurals are optionally allowed in compounds. He argued that if a pattern cannot be

learned from the input, then it must be an “innate structural property of the lexicon” (Gordon,

1985, p. 73). Therefore, because children clearly show a distinction between regular and

irregular nouns in this structure, level ordering must be innate. This conclusion about innateness

has been repeated frequently elsewhere (Clahsen, 1999; Hoff, 2001; Pinker, 1991, 1994, 1999).

However, we suggest that these findings are simply due to online processing conflicts

interacting with “soft” constraints of some sort, rather than to innate rules. If the requirement of

singular nouns in the first position of a compound is not a hard rule, but rather a violable

constraint, then there is another way to formulate the English pattern of compound formation:

English compounds obey the constraint that the first element is singular, regardless of whether

the semantics has stimulated the retrieval of a plural referent (e.g., toys, cookies). Thus, if a

compound such as cookie jar is called for, the retrieved cookies must be made singular before

proceeding. Irregular singulars and plurals differ more from each other than regular singulars and

plurals do; thus the irregular singular may be more difficult to access from its plural. This

explanation does not raise a learnability issue, as young children have plenty of examples of this

pattern in their early years (e.g., toy box, raisin box, jelly bean jar, cookie jar) and could well

have adduced such a rule by age 3, the youngest age Gordon (1985) tested.

What would be required of the structure of the mental lexicon for online processing to

contribute in such a way? Several models in the literature posit different storage for and

connections between forms for regular and irregular words (e.g., Allen & Badecker, 2002;

Pinker, 1991; Pinker & Prince, 1991/1994), differences in processing based on how similar two

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related forms are (e.g., Allen & Badecker, 2002), or constraint conflict and resolution (Haskell et

al., in press) – all of which could involve real-time processing impacts that result in differing

results for regulars and irregulars that do not depend on innateness or level ordering. Thus the

production of compounds like “mice-eater” could be a result of processing difficulty or an online

processing conflict (Bybee & Slobin, 1982; Menn, 1996). That is, it is harder in a language like

English, in which regularity = affix and irregularity = stem change, to “strip off” the stem-change

plural morpheme of an irregular noun than the affix plural of a regular noun. In Gordon’s (1985)

experiment the children were always primed with the plural of the first noun of the compound,

right before they had to produce the compound. Under the hypothesis proposed here, online

processes would need to detect and remove the plural morpheme to construct the noun-noun

compound. Detecting and removing the plural would be more difficult for irregular nouns –

difficult enough that sometimes these processes would not succeed before the output was made.

This difficulty should show up in two ways: First, the already observed predilection of both

adults and children to produce (or at least accept) the irregular plural noun in compounds more

often than the regular plural (predicted by both Gordon’s and our explanations), and second, a

longer time to produce such a compound with a singular first noun when given an irregular plural

as input (predicted by our explanation). Indeed, it ought to be harder in general to produce the

singular when the plural is already in mind, for words that have a non-transparent singular-plural

relationship between their forms (or, for that matter, to produce the plural when the singular is in

mind).

In summary, if processing factors can explain the observed behavior in noun-noun

compounds, then the following predictions can be made: Irregular plurals will be produced in

compounds more often than regular plurals; it should take longer to produce such a compound

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with a singular first noun when given an irregular plural as input than it would with other inputs;

and it ought to be harder in general to produce a form of a word when the opposite form is

already in mind, especially for words that have a formally non-transparent singular-plural

relationship.

Four experiments examined these predictions. The first two involved eliciting noun-noun

compounds in English; in Experiment 2 response times were also collected. The third and fourth

experiments used a task in which either the singular or the plural of a noun was evoked by means

of a picture (a simple line drawing), and a number cue was given to signal which of the two

forms (singular or plural) was supposed to be produced; sometimes the evoked form and the

required response matched in number, and sometimes they did not match. This task went beyond

forming compounds in that both singular and plural forms were explicitly required, rather than

just singular (which is implicitly, if not explicitly, required in English compound formation);

thus changing the form in both directions, rather than just one, could be tested. Experiment 3

employed English, and with a similar task Experiment 4 employed a miniature artificial

language, so that word frequency, regularity, and method of plural formation could be controlled.

Experiments 1 and 2

The purpose of Experiments 1 and 2 was to test a hypothesis about processing difficulty:

namely, that in the compound formation task it is harder (and thus takes more time) to produce a

singular form immediately after seeing the plural form of an irregular noun than it is after seeing

the singular form of an irregular noun or either form of a regular noun. The pattern of responses

(both experiments) and the time to respond (Experiment 2) were examined to address this

question. These experiments, though similar to that of Gordon (1985), differed in several ways,

one of which was that whereas Gordon only prompted the children with plurals in the X-eater

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questions, in Experiments 1 and 2 both singulars and plurals were used in the prompts.

Method

Participants

Twelve members of the Boulder community participated in Experiment 1 as volunteers;

24 University of Colorado students participated in Experiment 2 in partial fulfillment of

introductory psychology course requirements. All were native speakers of English.

Materials

Three types of target nouns were used (see Table 1 for full list): irregular, semantically

matched regular, and form matched regular (matched on form characteristics including initial

phoneme class and length). All were imageable English nouns. The set of target nouns was

expanded from the set used by Gordon (1985): More nouns were used, and in addition to

semantically-matched regular nouns, the form matched nouns were added. In Experiment 1 10

nouns of each type were used, both singular and plural, for a total of 60 target nouns. In

Experiment 2, all 60 nouns were used in trials, but trials for the woman and fungus sets were later

treated as fillers (due to the difficulty of scoring the woman/women trials and for balance

considerations), resulting in 48 target nouns. Noun sets were equated on word frequency.

Fill-in-the-blank sentence frames were used to elicit noun-noun compounds. Agentive

(Experiment 1) and container (both experiments) frames were used (examples in Figure 1). The

agentive frames resulted in compounds ending in follower/catcher/ painter/watcher, and the

container frames resulted in compounds ending in bowl/box/crate/tub. Appropriate verbs were

used in the sentence frames for each agentive or container noun.

Procedure

In Experiment 1 the response was written; in Experiment 2 the response was spoken, with

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response times collected by a computer. Participants saw fill-in-the-blank sentence frames and

responded with noun-noun compounds. In Experiment 1, sentences were presented 10 to a page

(six pages total); each noun was used once as a target, with either the agentive frame or the

container frame (counterbalanced across participants; each saw 30 of each type of frame). The

intended written response was the first noun of the noun-noun compound, based on the target

noun in the sentence. In Experiment 2, stimuli were presented on an iMac computer; spoken

responses and response times were recorded with a voice key. Each noun was matched with each

of the four containers. Compound trials were intermixed with single word trials. The intended

spoken response for compound trials was the whole compound, using the target noun and

container as the two nouns of the compound. Responses were scored based on the grammatical

number of the target noun: singular, plural, or other (if a noun other than some form of the target

noun was used); trials scored as “other” were excluded from the data analyses.

Design

The dependent variables were the proportion of singular out of singular and plural

responses and (in Experiment 2) the time to produce a singular response (for trials in which the

response was singular). Medians of response times were used to eliminate any effects of

skewness of response time data. Factors (all within-participant) were noun type (irregular,

semantic match regular, form match regular), stimulus noun number (singular, plural), and

sentence frame (agentive, container; Experiment 1 only). In Experiment 1, each noun, in both the

singular and plural forms, was seen in 1 trial, for a total of 60 responses. In Experiment 2, each

of the 48 target nouns, both singular and plural forms, was paired with each of the 4 containers,

for a total of 192 scored responses. Results were analyzed with a 2 2 3 (Experiment 1) or a

2 3 (Experiment 2) repeated measures analysis of variance. (For complete results including

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analyses with items as a random factor and minF', please see Buck-Gengler, 2003; here only the

analyses with participants as a random factor are reported.)

Results

In general, results not reaching the .05 level of significance are not reported for any of the

experiments.

Experiment 1

The main question of Experiment 1 was: Under what circumstances did participants not

use the singular form of the stimulus noun? As one would expect, the singular response was

given significantly less often overall when the stimulus noun was plural (M = .904) than when

the stimulus noun was singular (M = .988) [F(1, 11) = 10.52, MSE = .024, p = .008]. Also, as

expected, the response was singular significantly less often when the stimulus noun was an

irregular noun (M = .842) than when the stimulus noun was either a semantic match regular (M =

1.000) or a form match regular (M = .996) [F(2, 22) = 14.35, MSE = .027, p < .001]. Post-hoc

Newman Keuls tests confirmed that the proportion of singular responses for irregular nouns

differed from those for regular nouns, but the response proportions did not differ between the

two types of regular nouns.

Most interestingly, the interaction (see Figure 2) between number and noun type is

significant [F(2, 22) = 9.72, MSE = .024, p < .001]: When the trial contained an irregular plural

stimulus noun, the response was singular only 72.0% of the time, whereas the singular was used

between 96.5% and 100% of the time for the remaining five combinations.

The interaction of sentence frame and noun type was significant [F(2, 22) = 5.97, MSE

= .004, p = .009], reflecting the fact that the agentive frame had more singular responses than the

container frame for irregular noun trials [agentive M = .877, container M = .808] but not for trials

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with either type of regular noun [agentive, semantic match M = 1.000, agentive, form match M

= .992, container, semantic match M = 1.000, container, form match M = 1.000].

Experiment 2

In Experiment 2, the additional question was whether it took longer to produce a singular

response when the stimulus was an irregular plural than when it was another kind of stimulus.

Proportion of trials with singular first noun responses. The first analysis examined how

many responses used a singular first noun (out of responses that were either singular or plural),

no matter what the grammatical number of the stimulus. Whereas 92.1% of all semantic match

trials and 93.2% of all form match trials were responded to with the singular form of that noun,

only 60.4% of all trials with an irregular target noun were responded to with the singular form

[F(2, 46) = 127.17, MSE = .013, p < .001]. Of trials with a singular target noun, 99.2% of the

responses were also singular, whereas only 64.6% of the trials with a plural target noun were

responded to with the singular form [F(1,23) = 72.91, MSE = .053, p < .001].

Again, what is interesting is the interaction between these two factors [F(2,46) = 107.78,

MSE = .014, p < .001]. As can be seen in Figure 3(A), when the trial contained an irregular

plural target noun, the response was the singular form only 22.3% of the time (thus, 77.7% of the

responses were plural). For all five of the other combinations, the singular form was used

between 85.7% and 99.2% of the time. This result confirms earlier findings, notably those of

Gordon (1985), that irregular plurals are readily produced as the first noun of noun-noun

compounds in response to this type of elicitation frame.

RTs to singular first noun responses. The RT analysis examined the time to respond in

ms with a singular form to sentences containing either singular or plural irregular target nouns

(e.g., to respond mouse box when shown either “a BOX for transporting a MOUSE is a ______”

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or “a BOX for transporting MICE is a ______”), compared to the time to respond with a singular

form to sentences containing either a singular or plural regular target noun (e.g., to respond rat

box when shown either “a BOX for transporting a RAT is a ______” or “a BOX for transporting

RATS is a ______”). This analysis included only those trials in which the response was singular;

thus fewer trials contributed to the irregular plural cell than to the other cells (as seen in Figure

3(A)). Seven participants responded with a plural 100% of the time when given an irregular

plural stimulus and their data had to be excluded from this analysis.

RTs for the semantic match trials (695 ms) and the form match trials (691 ms) were

significantly faster than those for the irregular trials (809 ms) [F(2, 32) = 15.90, MSE = 961, p

< .001]. RTs for singular-stimulus trials (687 ms) were significantly faster than for plural-

stimulus trials (777 ms) [F(1, 16) = 24.13, MSE = 8658, p < .001]. Most interestingly, the

interaction between these factors, seen in Figure 3(B), was also significant [F(2, 32) = 12.82,

MSE = 9303, p < .001]. As can be seen in the figure, the irregular plural stimuli had the slowest

RT; all other forms were responded to much more quickly. As in Experiment 1, post hoc tests

confirmed that there was no difference in either measure between the two kinds of regular nouns.

Discussion

Gordon’s (1985) results, that plural is used more often when the immediately preceding

noun is an irregular plural than a regular plural (or a singular), was replicated in Experiments 1

and 2, although the proportion of plural responses to irregular plural stimuli was much greater in

Experiment 2 than in Experiment 1. Moreover, in Experiment 2 we found that even when the

singular was successfully produced, it took longer when the preceding noun was an irregular

plural than for any other type of noun. This second finding is not predicted by the standard

accounts. In other words, preference for producing irregular plurals as first elements of

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compounds in such elicitation tasks can therefore be explained by processing difficulty: For

example, goose is harder to access from geese than duck is from ducks (as might be predicted by,

e.g., Allen & Badecker, 2002, or Levelt, Roelofs, & Meyer, 1999).

Experiment 3

Experiments 1 and 2 were designed to see if it was harder to produce a singular from a

plural when the stimulus was irregular than when it was regular. Experiments 3 and 4 test the

more general hypothesis that it is more difficult to produce either the singular or the plural when

the opposite form is in mind, and that this difficulty is greater with irregulars than with regulars.

Method

Participants

Sixteen University of Colorado students participated in Experiment 3 in partial

fulfillment of introductory psychology course requirements. All were native speakers of English

and had not participated in the earlier experiments.

Materials

The stimulus nouns used in Experiment 3 (Table 2) were the singulars and plurals of the

eight irregular nouns used in Experiment 2, along with eight regular nouns matched on length,

frequency, and first letter (not necessarily phoneme, because the responses were typed), for a

total of 32 words. Pictures of both one and several of each item were used as stimuli. (Most

“plural” pictures were of two of the item, although some had three or four of the item and the

picture for teeth was of a set of teeth.) In the main task, each picture was accompanied by a

number cue (either “one ____” or “four ____”) to indicate that the required response was either

singular or plural.

Procedure

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First, participants were familiarized with the set of pictures and their associated words.

They saw each picture separately with its word, and typed the word; the entire set was repeated

twice in two different random orders.

In the main task each stimulus picture was crossed with each response number cue,

giving a total of 64 trials. A trial consisted of a picture cue and number cue; the participant typed

the word associated with the picture but matching the number cue (required response) in

grammatical form. Thus, if a picture of four trees was shown along with “one ____”, the required

response was “tree”. In half the trials, the grammatical number of the picture and required

response matched, and in half they did not.

Stimuli were presented on an iMac computer, and responses were typed; pressing the

ENTER key concluded the entry. (Half of the participants also heard the word matching the

picture pronounced, and the other half did not; however, this factor did not influence any

analyses and so was dropped from the analyses reported here.)

Design

Only trials in which the word was typed entirely correctly with no backspacing, and with

the same grammatical number required by the number cue, were included in the response time

analysis. The main dependent measure was the response time per letter. This measure was

computed by taking the total time to type the word (measured from the time the picture and

number cue were presented on the screen through the time to respond with the final letter of the

word, but not including the ENTER key) and dividing by the number of letters in the word; this

adjusted measure allows the direct comparison of response times for words of different lengths.

As in Experiment 2, medians of response times were used to eliminate any effects of skewness of

response time data.

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Factors (all within-participant) were the noun type (irregular, regular), required

grammatical response number (singular, plural), and match condition (match = the grammatical

number of the cue picture and the number cue matched; mismatch = those numbers did not

match). Results were analyzed with a 2 2 2 repeated measures analysis of variance.

Results

The letters of regular nouns (405 ms) were typed faster than those for irregular nouns

(459 ms) [F(1, 15) = 46.36, MSE = 2040, p < .001]. Extra response time per letter was needed

when the grammatical numbers did not match (448 ms) beyond the time taken when they did

match (416 ms) [F(1, 15) = 12.29, MSE = 2557, p = .003].

Noun type interacted significantly with required response number as can be seen in

Figure 4(A) [F(1, 15) = 5.98, MSE = 2908, p = .027]. It took less time on average to type letters

of irregular singulars than letters of irregular plurals, but for regular nouns, the letters were typed

more quickly on average in plurals than in singulars. Individual t-tests comparing the times for

singular and plural for each noun type reveal that the 15 ms difference between the irregular

forms was not significant [t(15) < 1] whereas the 31 ms difference between regular singulars and

plurals was significant [t(15) = 3.683, p = .002]. One reason for this difference is that the time

for the extra -s on regular plurals was always shorter than the overall average time per letter,

because of the contribution of the response time for the first letter (which was always longer).

As noted, the main effects of noun type and match were both significant. However, the

interaction between these two factors only approached significance [F(1, 15) = 3.23, MSE = 987,

p = .092]. As can be seen in Figure 4(B), the extra response time needed when cue and response

numbers did not match was greater for irregular nouns (41 ms) than for regular nouns (21 ms).

Both differences were significant by paired t-tests [irregular: t(15) = 3.56, p = .003; regular: t(15)

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= 2.30, p = .036].

Discussion

The main result of this experiment is that additional time is required to generate the

correct response when the picture number and response number do not match than when they do,

and this additional time to respond is even longer for irregular nouns than it is for regular nouns

(although the interaction is only marginally significant). Put another way, it appears that for

regular nouns, it is harder to generate the opposite form than the same form from a given

stimulus, and for irregular nouns, it is even more difficult to change from plural to singular, or

the reverse. These results agree with and expand upon the results from Experiments 1 and 2.

Irregular noun singulars and plurals differ more from each other, and in different ways, than do

regular noun singulars and plurals. If that difference has any effect at all in online processing, it

is more likely to make it harder to access the opposite form when it differs more, thus resulting

in longer response times.

Experiment 4

Natural languages have certain confoundings between regularity and other factors such as

word frequency, length, morphological patterns, and individual word idiosyncrasies. In addition,

for example in English, irregular plurals are realized in several different ways. Thus, to remove

as many of those confoundings as possible, and to make the differences between regulars and

irregulars as clear as possible, Experiment 4 was designed with the same task as Experiment 3,

but employing a miniature artificial language (as in the study by Bybee & Newman, 1995), in

which word length and form were controlled, and frequency and the method with which plurals

are formed were manipulated.

Method

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Miniature artificial language

Words used in the miniature artificial language (MAL) were designed to control for both

form and frequency. The singular forms were all CVCV, where each C was one of {b, p, d, t, g,

k, m, n, z, s, v, f} and each V was one of {a, i, o, u}. Neither C nor V was repeated in a given

word. With 12 consonants and 4 vowels, there are 48 possible CV syllables. Words were

constructed such that each of the possible 48 syllables was used exactly once as either a first

syllable or a second syllable. Familiar words (e.g., tofu) were excluded. There were 24 words

(singular form) in all.

Two versions of the MAL were created, based on how plurals were formed (see also

Bybee & Newman, 1995). In the prefix version (more English-like), regulars were formed by

prefixing e (e-CVCV) and irregulars by infixing an arbitrary vowel (other than e) after the first C

(C-#-VCV, where # was the particular vowel for that word). In the infix version, regulars were

formed by infixing e (C-e-VCV), and irregulars by prefixing the arbitrary vowel (#-CVCV).

Frequency was manipulated by how often a word was presented in the learning phase; high

frequency words were presented four times as often as low frequency words. Frequency and

regularity (noun type) were independently varied, and crossed with each other. There were 12

low frequency regulars and four each of high frequency regulars, low frequency irregulars, and

high frequency regulars. A complete list of MAL words is given in Table 3. One purpose of

using prefixes and early infixes rather than suffixes, as used in English, was to make errors of

number (i.e., when the response was begun with one form but changed to the other) easier to

detect than in English; in the previous experiments it is possible that participants could have

begun responding with one form when intending the other and caught the error before the output

showed it.

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Participants

Twenty-four University of Colorado students participated in Experiment 4 in partial

fulfillment of introductory psychology course requirements. All were native speakers of English

and had not participated in the earlier experiments.

Materials

As in Experiment 3, pictures of both one and several of each item were used as stimuli. In

Experiment 4, however, the pictures were paired with MAL words as described earlier. In the

main task, each picture was accompanied by a number cue (either “1 ____” or “4 ____”) to

indicate that the required response was either singular or plural. All concepts were regular nouns

in English.

Procedure

Participants first had to learn the words of the MAL well enough to use them in the main

task. Learning the MAL involved repeated cycles of typing a word, being quizzed on the 12

words most recently seen, and being tested on the entire set of 48 words. The type/quiz/test cycle

(described in more detail below) was repeated until a criterion of 90% correct on the test was

reached. When the criterion was reached, the participant proceeded to the main task. The main

task was equivalent to that of Experiment 3.

Learning the MAL. The typing/quiz/test cycle had several parts. The 48 words (singular

and plural forms of the 24 MAL words) were divided into 8 subsets of 12 words, with high

frequency words occurring 4 times as frequently as low frequency words. Subsets contained a

carefully balanced mix of high and low frequency words, singulars and plurals, regulars and

irregulars. On an individual trial, the participant saw a picture and associated MAL word, and

typed the word. After the subset was presented once or twice (depending on where in learning

“MICE TRAP” 20

the participant was), the participant was quizzed by being shown each picture and typing in the

word. Feedback and correction were given. The typing/quiz phases were self-paced to allow the

participants to learn the picture-word associations and also to learn from their mistakes. After all

eight subsets were seen and quizzed, all 48 pictures were tested (with feedback and correction).

At the end of each round of testing, the participant was told how he or she was doing compared

to earlier rounds and also earlier participants. The criterion of 90% was based on words typed

correctly with backspacing allowed. All participants learned the words of the MAL to criterion in

7 rounds or fewer (M = 3.17); almost half (11 of 24) of the participants learned to criterion in 2

rounds.

During the learning phase (in which both picture and word were shown), the words were

pronounced by the computer, but not in the quiz, test, or main task (in which the task was to

generate the word from the picture).

Design

Only main task trials in which the word was typed entirely correctly with no backspacing,

and with the same grammatical number as the number cue, were included in the response time

analysis. The dependent measure examined was the response time per letter, as described for

Experiment 3. As in Experiments 2 and 3, medians of response times were used to eliminate any

effects of skewness of response time data.

The main analysis is a 2 2 2 2 2 mixed factorial analysis of variance. The first

factor, language group (i.e., pluralization type: regular-prefix/irregular-infix,

regular-infix/irregular-prefix), was varied between participants (referred to as the prefix and infix

groups, respectively). The remaining factors, required grammatical response number (singular,

plural), match condition (match, mismatch), word frequency (high, low), and noun type (regular,

“MICE TRAP” 21

irregular), were varied within participants.

Results

Letters in regular nouns were typed faster (663 ms) than those in irregular nouns (721

ms) [F(1, 22) = 7.00, MSE = 45828, p = .015], and letters in nouns in match trials were typed

more quickly (670 ms) than those in mismatch trials (715 ms) [F(1, 22) = 5.83, MSE = 33450, p

= .025]. Figure 5(A) (cf. Figure 4(B) from Experiment 3) shows the interaction of these two

main effects; the interaction is not significant [F(1, 22) < 1].

In addition, the effect of noun type was only found in the (regular-)prefix group, as can

be seen in Figure 5(B) [F(1, 22) = 13.62, MSE = 45828, p = .001]: The (regular-)prefix group

typed letters in irregulars (which were infixed) 138 ms slower than those in regulars [t(11) =

4.31, p = .001] whereas for the (regular-)infix group the 23 ms difference between regulars and

irregulars (which were prefixed) was not significant [t(11) < 1].

Looked at another way, this interaction is the equivalent of a main effect of where the

plural is added (prefix vs. infix). Participants typed letters faster in words with prefixed plurals

(for both singular and plural responses) than in words with infixed plurals. The difference was

smaller for the infix group, who had more exposure to infixed plurals (because regulars

outnumber irregulars), than for the prefix group.

Discussion

In this experiment, many of the problems in natural language that can confound results

were reduced, controlled, or eliminated. In Experiment 3, there was a marginal interaction of

noun type and match condition, in addition to significant main effects of those factors. Moreover,

the interaction between noun type and match was also seen in Experiments 1 and 2. In

Experiment 4, there was only a main effect of each of these factors. The difference between

“MICE TRAP” 22

regular and irregular English nouns seen in that interaction in Experiment 3 could be due to

confounded differences eliminated in Experiment 4, in particular, word frequency and individual

word idiosyncrasies.

For the correct answers, two factors had major impacts on the response time for a word.

Frequency did not play a role in how fast a word was typed; in some sense these words are all

extremely low frequency as compared to the word knowledge a participant already has, and thus

frequency effects often seen in natural languages (e.g., in RTs) were not found in Experiment 4.

Response number also did not play any role, likely because of the controls on frequency and

word length in the MAL, and the use of RT per letter rather than total RT. Importantly, however,

both noun type and whether the number in the picture matched the required response number

given in the cue influenced the time to enter the correct response.

That regulars were entered more quickly than irregulars, at least for the prefix group,

indicates that access to regular nouns is quicker than to irregular nouns, especially when the

regular plurals are more segmentable. Also, note that whereas token frequency was not a

predictor of RT, type frequency is still confounded with regularity (noun type), as it is in a real

language. In the present design, which idealizes the English frequency pattern, the frequency of

the regular plural affix or infix is much higher than the marker for any particular irregular plural,

thus potentially contributing to the overall speed differences for the noun types.

Match condition also being significant reinforces the finding from the earlier

experiments: It takes longer to produce the opposite form than the same form from a given form.

In Experiment 4, the amount of overlap between singular and plural was much more similar for

regulars and irregulars than in English, thus both noun types show this effect to a similar degree.

In English the differences are much greater, and the ways in which irregulars are formed show

“MICE TRAP” 23

much more variety in the change to the base form.

Prefixing was easier for both groups than infixing; infixed words, both singular and

plural, suffered compared to prefix words, especially for the prefix group. Thus it appears that it

is indeed somewhat harder to change the body of a word rather than simply appending to one end

or the other (in contrast with Bybee & Newman’s, 1995, findings). Both groups in this task

found prefixing easier (in terms of time to type the letters of the words) than infixing, even the

infix group for which prefixes were varied and less frequent rather than identical for all forms.

Thus, as in English, when the regular plural morpheme is easily segmentable, there is a

difference between regular and irregular nouns, in addition to the separate effect of whether the

cue number and picture number matched. However, when the regular morpheme is not easily

segmentable, the only effect is that of matching.

General Discussion

In the first two experiments, the general pattern of responses from children seen in

Gordon’s (1985) experiment was replicated with adults. That is, regular plurals were rarely

produced as first elements of compounds, but irregular plurals were used significantly more

often. Experiment 2 also provides RT data, as well as a look at whether the pattern is the same or

modified under rather different experimental conditions. With these additional data it is clear that

even when the speaker comes up with the “correct” (singular) response, there is a real difference

between going from a plural stimulus to a singular response with an irregular as opposed to a

regular noun. For regulars, it was as easy, in terms of time, to go from the plural to the singular

as to produce the singular from itself (no change; equivalent to identity in priming tasks). But for

irregulars, it was much more difficult to go from plural to singular than simply to use the singular

(when the singular was shown). This pattern seems to be evidence of a conflict or competition of

“MICE TRAP” 24

some sort that happens only when the stimulus and the response differ from each other more than

regular singulars and plurals differ.

The third experiment looked at the general issue of producing the same or the opposite

form from a given noun. We found a time cost in changing number in both directions, compared

to responding with a form with the same number as the picture on the screen. The cost was found

for both regulars and irregulars, unlike in Experiment 2, but the cost was numerically greater for

irregular nouns. Also, overall, regular responses were faster than irregulars.

The fourth experiment utilized a miniature artificial language (with the same task as in

Experiment 3) to eliminate or minimize other potential confoundings found in natural languages

such as frequency, individual form idiosyncrasies, how the plurals are formed, and so on.

Participants produced even more clearly the main results from Experiment 3: Regulars were

typed faster than irregulars, and responses were typed more quickly if the number of the picture

matched the required response. Frequency was manipulated in this experiment for comparison

with natural language, but it had no direct effect on RT. What was not found in this experiment is

the interaction between noun type and match condition (cf. Experiment 3) or cue number (cf.

Experiments 1 and 2). Thus it is likely that the factors that were controlled in Experiment 4,

namely type frequency, token frequency, way in which the plural is formed, word length, and

other form factors, contribute in a natural language to the differences seen between regulars and

irregulars in the earlier experiments, especially Experiments 1 and 2.

The results from Experiment 4, in combination with those from Experiments 1-3, point to

the main factor in all three tasks being match rather than regularity. It is likely that what caused

the difference in Experiments 1 and 2 between regulars and irregulars were some or all of the

confoundings found in English. The interaction between match and regularity already started

“MICE TRAP” 25

going away in Experiment 3 when the task was made bi-directional and more

abstract/metalinguistic; in Experiment 4 the fact that “regulars” were faster than “irregulars” was

most likely due to their greater type and token frequency in the learning phase. Frequency itself,

however, did not matter. In the first two experiments especially, the sheer overwhelming

frequency of the regular morpheme, coupled with its ease of segmentability, is likely what made

regular singulars so easy to produce (Bybee, 1995), rather than a difference in regular versus

irregular, rule use versus memory lookup, or adhering to level-ordering dictates. The results of

Experiment 4 also support the idea that segmentability plays a role in ease of use – only regulars

that were prefixed, and thus easily segmentable, had an advantage over irregulars. If English

regulars were as difficult to segment as English irregulars are, or were less frequent (or even of

similar frequency to irregulars), as in German, then it is likely that regulars would not have the

advantage they do in the compound generation/depluralization task.

From these results we conclude that the frequently reported preference for irregular plural

as first element of noun-noun compounds can be explained by processing factors (i.e., the

accessibility of the singular from the plural) that hold for both children and adults, and in both

natural and artificial languages. No appeal to innate grammar is required to explain the similarity

between child and adult performance on this aspect of linguistic behavior.

More generally, the closer two forms of the same word (lemma) are to each other, the

faster one will be accessed from the other (Bybee & Slobin, 1982). Unlike English, the MAL

ensured that the difference in form between singular and plural was equivalent for both regulars

and irregulars. With this control, we have teased apart the issues of regularity and similarity, and

have shown them to have separate, non-interacting effects.

“MICE TRAP” 26

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Author Note

The research presented in this article represents the main findings in the first author’s

dissertation, which was conducted under the joint supervision of the other two authors. More

complete details may be found in the dissertation, which will be available via the normal routes

as well as online as a pdf file.

We thank James Kole, Erica Wohldmann, and Katrina Raybun for their assistance in

scoring the responses in Experiment 2, Jon Roberts and Ernie Mross for programming assistance,

David Underwood for preparing the picture stimuli, and Holly Krech Thomas for recording the

spoken words used in Experiment 3.

This research was supported in part by Army Research Institute Contracts DASW01-99-

K-0002 and DASW01-03-K-0002 and Army Research Office Grant DAAG55-98-1-0214 to the

University of Colorado (Alice Healy, Principal Investigator; Lyle Bourne, Co-Principal

Investigator). This research was also supported in part by a Student Research Award from the

Institute of Cognitive Science (University of Colorado at Boulder) to the first author.

“MICE TRAP” 30

Table 1

Stimulus Nouns (Singular and Plural Forms) Used in Experiments 1 and 2, by Type

Regular noun

Irregular noun Semantic match Form match

Singular Plural Singular Plural Singular Plural

mouse mice* rat rats* nail nails

tooth teeth* bead beads* tape tapes

foot feet* hand hands* hat hats

goose geese* duck ducks* bell bells

man men* baby babies* letter letters

louse lice fly flies knight knights

child children doll dolls chain chains

ox oxen horse horses ax axes

woman women monkey monkeys watch watches

fungus fungi fern ferns frog frogs

*From Gordon (1985)

“MICE TRAP” 31

Table 2

Irregular and Matched Regular Nouns, Both Singular and Plural Forms, Used as Stimuli in

Experiment 3

Irregular noun Regular noun

Singular Plural Singular Plural

child children car cars

foot feet fork forks

goose geese gun guns

louse lice letter letters

man men match matches

mouse mice moon moons

ox oxen owl owls

tooth teeth tree trees

“MICE TRAP” 32

Table 3

List of Words in MAL Used in Experiment 4

Regularity

Frequency Regular Irregular

High tree bidu ebidu / beidu

moon tosa etosa / teosa

flag nuvi enuvi / neuvi

canoe fazo efazo / feazo

dog muba miuba / imuba

match gifo gaifo / agifo

fork koni kuoni / ukoni

turtle dasu doasu / odasu

Low letter vabo evabo / veabo

key zadi ezadi / zeadi

chair nafu enafu / neafu

box migu emigu / meigu

shoe zika ezika / zeika

cow goma egoma / geoma

drum tuno etuno / teuno

bell kupi ekupi / keupi

candle buta ebuta / beuta

glove doti edoti / deoti

lantern sivo esivo / seivo

shovel pozu epozu / peozu

gun figa faiga / afiga

snake paki poaki / opaki

tent vumo viumo / ivumo

bucket sopu suopu / usopu

Note. First word in a line is the concept in English; second word is the singular form in the MAL;

third word is the plural form in the prefix version of the MAL; and fourth word is the plural form

in the infix version of the MAL.

“MICE TRAP” 33

Figure Captions

Figure 1. Sentence frames and examples of stimuli in Experiments 1 and 2. Note. Exp. =

Experiment.

Figure 2. Proportion of singular responses by noun type and grammatical number of the stimulus

noun in Experiment 1.

Figure 3. Results for Experiment 2. (A) Proportion of singular response by noun type and

grammatical number of the stimulus noun. (B) Response times in ms for singular responses.

Figure 4. Results for Experiment 3. (A) Interaction between noun type and required response for

response time per letter measure. (B) Interaction (marginal) between noun type and match

condition for response time per letter measure.

Figure 5. Results for Experiment 4. (A) Interaction (non-significant) between noun type and

match condition for response time per letter measure. (B) Significant interaction between

language group and noun type for response time per letter measure. Labels indicate the particular

type of plural formation represented by that bar.

“MICE TRAP” 34

Agentive frame (Exp. 1):

Someone who VERBs (a/an) STIMULUS NOUN is a/an ____ VERBer

Container frame (Exp. 1):

A CONTAINER (for) VERBing (a/an) STIMULUS NOUN is a/an ______ CONTAINER

Container frame (Exp. 2):

a CONTAINER (for) VERBing (a/an) STIMULUS NOUN is a/an ______

Examples:

Someone who follows a hat is a ____ follower (Exp. 1)

Someone who catches mice is a _____ catcher (Exp. 1)

A crate for shipping a child is a _____ crate (Exp. 1)

A tub holding chains is a _____ tub (Exp. 1)

a BOWL containing a MAN is a ______ (Exp. 2)

a BOX for transporting AXES is an ______ (Exp. 2)

a CRATE for carrying a BEAD is a ______ (Exp. 2)

a TUB holding MICE is a ______ (Exp. 2)

Figure 1

“MICE TRAP” 35

Figure 2

“MICE TRAP” 36

(A)

(B)

Figure 3

“MICE TRAP” 37

(A)

(B)

Figure 4

“MICE TRAP” 38

(A)

(B)

Figure 5