ROMANIAN JOURNAL OF

EXPERIMENTAL APPLIED PSYCHOLOGY

VOL. 6, ISSUE 4 – www.rjeap.ro

OPTIMAL VIEWING POSITION EFFECT OF CONNECTING

AND UN-CONNECTING LETTERS WITHIN LETTER-

STRING IN ARABIC

DEIA GANAYIM a

The Arab Center for Mind, Brain & Behavior (ACMBB)

Abstract

The current study investigates the role of Arabic letter visibility as a possible

cause of the Optimal Viewing Position-OVP effect. We used connecting and un-

connecting Arabic letters of different shapes (basic, initial, medial, final) placed at

the various possible positions within connecting letter string of لs (للللللللللل)

(Experiment 1) and within un-connecting letter string of اs (ااااااااااا) (Experiment 2).

In order to investigate whether performance on the visual identification task is

modulated by letter type, we presented each of the connecting and un-connecting

letter targets in each of the ten stimulus positions across the array so as to produce

a mean RT (ms) for each of the letter types. Using the initial fixation paradigm

enabled us to compare Reaction times with correctly identified letter targets

appearing in the different possible positions within letter-string.

The findings of the present experiments demonstrated that visual letter

recognition is influenced by: (i) the letters' type (connecting, un-connecting), as

connecting letters are easier to recognize than un-connecting letters; and (ii)

letters' shape (basic, initial, medial, final), as medial and final are harder to

recognize than basic and initial letter shapes, (iii) letter string's type, as reading

rates were longer for letter stimuli that have been embedded within a connecting

letter string compared to an un-connecting letter string with inter-letter spacing,

(iv) visual field, as reading rates were longer for letter stimuli that have been

presented in LVF compared to RVF, (v) eccentricity, as letter reading rates were

correlated with its eccentric placement across the letter string.

Keywords: Arabic, Crowding, Optimal viewing position, Visual recognition,

Connected/Un-connected.

*Corresponding author: Deia Ganayim Email: info@acmbb.org.il

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1. INTRODUCTION

It is now generally accepted that visual word recognition in languages with

alphabetical orthographies involves identity processing of a word’s component

letters. Thus, text cannot be read if letters or words are not resolved (Falkenberg,

Rubin, & Bex, 2007). Several researchers also agree that much of this processing

should be performed in parallel (e.g., Grainger, 2008; Grainger & Jacobs, 1996;

McClelland & Rumelhart, 1981).

Adelman et al. (2010) showed that among adult readers, letter identity

encoding starts during the first 25 ms of printed word processing for all string

positions simultaneously. However, the authors showed that while processing was

initiated over the whole word letter string in parallel, all letters were not identified

at the same level of efficiency (Reilhac, Jucla, Iannuzzi, Valdois & Démonet,

2012).

What factors influence our ability to identify letters? This question is

important because it will help develop our understanding of the very first phase of

reading processes during which visual feature information is mapped (in parallel)

onto position-coded letter identities in both central and peripheral vision (Grainger

& van Heuven, 2003; Marzouki et al., 2013).

One particularly useful approach for addressing this issue is to examine the

process of letter identification within letter strings. In this way, we can gather

information about letter-level processing while minimizing the influence of higher-

level phonological and semantic processes. The assumption here is that during

visual word recognition, some form of letter-level processing must be performed

before higher order codes come into play (Grainger, Granier, Farioli, Van Assche,

& van Heuven, 2006; Grainger & van Heuven, 2003).

One well-established phenomenon in research investigating letter string

perception is that when fixating on the center of a letter array, performance is

optimal for the central letter, and then, drops as a function of eccentricity

(Averbach & Coriell, 1961; Butler, 1975; Butler & Merikle, 1973; Haber &

Standing, 1969; Merikle, Coltheart, & Lowe, 1971; Merikle, Lowe, & Coltheart,

1971; Mewhort & Campbell, 1978; Nazir, Ben-Boutayab, Decoppet, Deutsch, &

Frost, 2004; Schwantes, 1978; Stevens & Grainger, 2003; Wolford &

Hollingsworth, 1974). This reflects a drop in visual acuity as a function of distance

from fixation (Taydgat & Grainger, 2009).

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Under some conditions, alphanumeric characters that are reliably identified in

isolation can no longer be identified, when closely surrounded by other optotypes

or contours (Bouma, 1970; Pelli et al., 2004; Pelli & Tillman, 2008). This effect is

known as crowding, lateral interference, or local contour interaction (Falkenberg,

Rubin, & Bex, 2007). The effect of lateral interference on letter identification is a

well-studied phenomenon in experimental psychology, with results showing that

target letters flanked by other letters to the left and/or right are harder to identify

than isolated letter targets (e.g., Bouma, 1970; Huckauf & Nazir, 2007; Grainger et

al., 2010). More recently, effects of lateral interference have been integrated within

a wider perspective of crowding effects on the processing of various types of visual

stimuli (e.g., Pelli et al., 2004; Pelli & Tillman, 2008; see Levi, 2008; Whitney &

Levi, 2011, for reviews). However, the vast majority of these studies have limited

their investigation to the effects of stimuli that are closest to the target and have

shown that target-flanker separation determines target identification accuracy.

Much of this work can be summarized by Bouma’s law (Bouma, 1970; Pelli &

Tillman, 2008), which states that critical spacing (i.e., the target-flanker separation

that allows target identification at a criterion level of accuracy) is a linear function

of target eccentricity. Therefore, it is possible that crowding reduces visibility of

adjacent letters or words (or increases spatial interference among them); this is the

process that likely slows reading (Falkenberg, Rubin, & Bexr, 2007).

The importance of understanding mechanisms involved in letter identification

within a letter string has been well illustrated by a recent finding showing that

increased letter spacing can facilitate reading in children with dyslexia (Perea et al.,

2012; Zorzi et al., 2012). Indeed, crowding is one factor known to have a large

influence on letter-in-string perception, and manipulating inter-letter spacing

modulates the amount of crowding. In the present study, we focused on one

specific aspect of crowding effects–the contribution of flanking element type

(connecting, un-connecting)–while examining possible interactions between

crowding effects and visual acuity during Arabic letter identification.

Another main finding from previous research on letter identification is that

there is an asymmetry in the visibility of letters to the left and right of fixation

(Bouma, 1973; Kajii & Osaka, 2000; Nazir, 1991; Nazir, Heller, & Sussmann,

1992; Nazir, Jacobs, & O’Regan, 1998). Nazir et al. (1992) measured letter

visibility at various distances from the left and right of fixation. A drop in

recognition performance depended not only on the distance from a fixation but also

on the side of the presentation. At the same distance from fixation, letters to the

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right of fixation were easier to recognize than letters to the left. This asymmetry in

letter perception was previously reported by Bouma (1973) for the first and last

letters of nonsense strings and has since been replicated for letters embedded in

digits (Kajii & Osaka, 2000). The present study assessed this phenomenon with

Arabic letters.

2. THE PRESENT STUDY

The present study provides a further exploration into the role of Arabic letter

visibility as a possible cause of the optimal viewing position (OVP) effect. Bouma

(1973) tested identification of the initial and final letters of random letter strings

(e.g., dvxmk) with the entire string presented to the left or right visual field. Nazir

et al. (1992) measured the visibility of letters embedded in a series of Xs. However,

the letters did not appear at every possible position in the series, and fixation was

only at the first or last letter in the series. Kajii and Osaka (2000) measured

identification of letters embedded in digits, but once again, the entire string was

presented to the left or right of a central fixation point (in their horizontal display

condition). Finally, traditional studies of letter-in-string visibility (e.g., Estes,

Allmeyer, & Reder, 1976) used only central fixations. Thus, to date, there are no

studies providing complete measures of Arabic letter visibility across all

combinations of fixation positions and letter-in-string positions. Our study was

designed to address this gap, while building on the classic work in this field in an

attempt to highlight some key, unresolved issues. We used connecting and un-

connecting Arabic letters of different shapes (basic, initial, medial, and final)

placed at various possible positions within connecting letter strings of لs (للللللللللل)

(Experiments 1) and within un-connecting letter strings of اs (ااااااااااا) (Experiments

2). In order to investigate whether performance on the visual identification task

was modulated by letter type, we presented each of the connecting and un-

connecting letter targets in each of the ten stimulus positions across the array to

produce a mean RT (ms) for each letter type. Using an initial fixation paradigm

enabled us to compare RTs with correctly identified letter targets appearing in

different possible positions within a letter-string.

The present study assessed precisely what factors are at play during the

computation of letter identities in the earliest phases of letter perception and

whether this processing does, indeed, depend on peripherally un-fixated vision.

This was of special interest when the OVP paradigm was employed to investigate

Arabic language with its unique visual features of connectedness (Table 1).

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The processes used for identifying letters within letter strings are adaptive to

the nature of the script to which the reader is exposed during reading acquisition

(Pitchford & Lefgeway, 2008). One feature of an alphabetic orthography, such as

Arabic, that may be extracted through a process of statistical learning is the

frequency with which letters appear within words (i.e., how often a particular letter

occurs in words, per se; Pitchford & Lefgeway, 2008). Arabic connecting letters

are of higher frequency (22 letters out of 28), than un-connecting letters (6 letters

out of 22) occurring in words. In previous studies, significant negative correlations

were found between the RT needed to detect a target letter and letter frequency. If

letter frequency is an orthographic property that influences the identification of

letters within letter strings, RTs should be faster for identifying connecting target

letters appearing in the string compared with un-connecting target letters that are

least frequent in written words.

The contribution of crowding among Arabic letters has not been

systematically studied; it remains unclear whether changes in letter type and letter

string type influence letter identification. Furthermore, a letter within a letter string

is (necessarily) at differing eccentricities. Thus, it is possible that part of the

decline in visual or perceptual span performance will be attributed to changes in

acuity or crowding with eccentricity.

Clearly, if crowding (as defined by Pelli, Palomares, & Majaj, 2004) is a key

factor affecting letter recognition, then recognition of isolated letters will be

affected by crowding to a lesser extent than letters presented within a letter string.

In particular, the type of letter string (connecting, un-connecting) will determine

the amount of lateral masking, and crowding interference will be larger for

connecting letter stings than un-connecting letter strings. Next, we argue that the

pattern of results found in the present study might be understood by considering the

constraints imposed on a specialized system for processing strings of letters in

Arabic. The key mechanism behind this account is crowding (see Levi, 2008, for a

recent review), and the central hypothesis is that crowding affects connecting and

un-connecting letters differently.

However, this letter identification is unlikely to be due to a single process. We

assume that one possible interpretation of the phenomenon is that it reflects the

conjoint influence of three factors: (a) the drop in visual acuity as a function of

distance from fixation, (b) the amount of lateral interference (crowding)

determined by the number of flanking letters (Bouma, 1970, 1973; Estes, 1972;

Estes, Allmeyer, & Reder, 1976; Haber & Standing, 1969; Van der Heijden, 1992),

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and (c) the difference in inter-hemispheric processing. Because of the first factor,

letter recognition becomes worse for letters that are farther from fixation. Because

of the second factor, recognition of letters flanked by a letter on each side is worse

than for letters with only one flanking letter. Due to the third factor, recognition of

letters presented to the right of fixation is better than letters presented to the left of

fixation.

Table 1. Letter stimuli used in the different experiments.

Unconnected Letters Connected Letters

Final Medial Initial Basic Final Medial Initial Basic

1 صي صيه يه ي د د صد صد

2 صه صهه هه ه و و صو صو

3 صن صنه نه ن ز ز صز صز

4 صم صمه مه م ر ر صر صر

5 صل صله له ل ذ ذ صذ صذ

6 صك صكه كه ك ا ا صا صا

7 صق صقه قه ق د د صد صد

8 صف صفه فه ف و و صو صو

9 صغ صغه غه غ ز ز صز صز

10 صع صعه عه ع ر ر صر صر

11 صظ صظه ظه ظ ذ ذ صذ صذ

12 صط صطه طه ط ا ا صا صا

13 صض صضه ضه ض د د صد صد

14 صص صصه صه ص و و صو صو

15 صش صشه شه ش ز ز صز صز

16 صس صسه سه س ر ر صر صر

17 صخ صخه خه خ ذ ذ صذ صذ

18 صح صحه حه ح ا ا صا صا

19 صج صجه جه ج ز ز ز ز

ثص صثه ثه ث و و صو صو 20

21 صت صته ته ت ذ ذ صذ صذ

22 صب صبه به ب ا ا صا صا

The hypotheses address the following: peripherally-non-fixated

connecting/un-connecting Arabic letters level within connecting letter strings and

un-connecting letter strings, at all ten possible letter fixation locations. For the

study questions related to the peripherally-non-fixated connected/un-connected

Arabic letter level, we addressed the following:

(1) Is readability affected by visual differentiations of the connecting\un-

connecting letterforms within a letter-string in Arabic in the peripherally-

non-fixated letter position? We expect that the un-connecting letters will be

named faster than the connecting letters as the former have almost the

same basic shape in every word position. Alternatively, the naming of

connecting letters may be faster than the un-connecting letters because

15

these letters are more frequent in words than un-connecting letters. This

pattern supports a letter frequency effect of letter recognition.

(2) Is connecting/un-connecting letter readability affected by visual

eccentricity in Arabic? We expect that the recognition performance for

letters will be a function of distance from fixation. Reaction times for

letters will increase as a function of eccentricity. This pattern supports the

visual acuity drop effect of letter recognition.

(3) Is connecting/un-connecting letter readability affected by the visual field

presentation in Arabic? We expect that recognition performance for letters

presented in the right visual field (RVF) will be better than for letters

presented in the left visual field (LVF). This pattern supports the inter-

hemispheric processing differentiation effect of letter recognition.

3. EXPERIMENT 1

Since a letter appears frequently within a multi-letter string, the present

experiment addressed the influence of the visual complexity of Arabic orthography

on letter identification OVP. More specifically, we assessed how connecting (or

un-connecting) letters presented in all possible left or right visual fields within a

multi-letter string of un-connecting letters would affect their identification. Thus,

the goal of the present experiment was to explore the OVP of connecting vs. un-

connecting letters within a multi-letter string of un-connecting letters in Arabic. An

initial fixation paradigm was used to present letters in the two visual fields (left,

right), according to their position in the word (basic, initial, middle, and final), and

within all letter fixation positions (1, 2, 3, 4, and 5). Participants were asked to read

(recognize) each presented letter. Participants’ performance was measured

according to accuracy rates and RTs for each letter condition. The main

experimental question was whether the OVP of Arabic letters within a multi-letter

string of un-connecting letters is dependent on letter type (connecting, un-

connecting), letter shape (basic, initial, middle, or final), and visual field

presentation (left, right).

3.1. METHOD

3.1.1. Variables

The independent variables were letter type (connecting vs. un-connecting),

letter shape according to its position in the word (basic, initial, middle, and final),

visual field (left, right), and initial fixation letter position (1, 2, 3, 4, and 5). The

16

dependent variables were accuracy rate and RTs for correct recognition. The

experimental matrix was a within-subjects quadric-factorial 2 × 4 × 2 × 5 design.

RVF + LVF

I

و و

I

و و

I

و و

I

و و

I

و و

I

5 4 3 2 1 + 1 2 3 4 5

Letter Position

Figure 1. Example of how letter position was manipulated in the left visual field (LVF) and right visual field (RVF).

3.1.2. Participants

A total of 22 university students participated in this experiment (average age:

22.2, SD = 3, 10 males and 12 females). All were native Arabic speakers, from a

middle range of socio-economic status, right-handed, displayed normal or

corrected-to-normal vision in both eyes, and had no history of neurological or

emotional disorders. No participant was formally diagnosed as having reading

impairments.

3.1.3. Stimuli

The stimuli were 2 lists of 22 letters each according to word type (connected,

un-connected) and presented in all letter shapes according to its position in the

word (basic, initial, middle, and final) (Table 1). The un-connecting letter ( ا ) was

not used because letters were in white 24 Simplified Arabic Fix font embedded

17

within a multi-letter string of 11 un-connecting " " ا on a black (اااا ب اااا)

background displayed on a PC screen.The letters were presented randomly.

3.1.4. Procedure

A CRT display was placed at a viewing distance of 60 cm from the

participant. The total number of trials was 960 . Each trial contained the following

steps:

1) Two vertical fixation lines were presented in the middle of the screen for

300 ms.

2) The letter stimulus within a multi-letter string of 11 un-connecting " " ا اااا )

was presented for 150 ms between the lines with the letter that was to (ب اااا

be fixated on placed in all five initial letter fixation positions for each

visual field.

3) The fixation lines remained on the screen until a voice key registered a

response or until a time-out of 1,500 ms was reached (Fig. 1). A break was

provided after 30 trials or whenever the participant indicated that (s)he

needed a break.

Figure 2. Time course of one trial in the letter central fixation task.

Participants received notice that there would be an Arabic letter withn a letter-

string. The importance of fixating between the two lines, when these lines were

presented, was stressed explicitly and repeatedly. Participants were asked to name

the letters as quickly and as accurately as possible. Participants were informed that

they could ask for a break whenever they wanted.

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Each participant was tested individually with a random presentation sequence

of the letters. The experimenter wrote the letter noted by the participant.

3.2. RESULTS

Accuracy percentage rates exceeded 99% in all conditions; therefore, an

accuracy analysis was not conducted. Differences in reading latencies between the

two types of letters listed in the 2 lists according to shape and position in the word

(basic, initial, middle, and final), visual field (left, right) and the initial fixation

letter position (1, 2, 3, 4, and 5) were analyzed with a repeated measures ANOVA.

The effect of letter type (connecting vs. un-connecting) was significant (F

(1,21) =10.56, p < 0.005). Reaction times for the connecting letters (Mean = 474,

SD = 103) were shorter than for the un-connecting letters (Mean = 494, SD = 105).

The effect of letter position (basic, initial, middle, and final) was significant

(F (3,19) = 9.59, p < 0.0005). Reaction times for the medial position letters were

similar to the final position letters but longer than for the basic and initial position

letters (Fig. 3, Table 2).

The effect of visual field (left, right) was significant (F (1,21) = 4.85, p <

0.05). Reaction times for letters presented in the right visual field (Mean = 475, SD

= 103) were shorter than for letters presented in the left visual field (Mean = 493,

SD = 109).

The effect of letter fixation position (1, 2, 3, 4, and 5) was significant (F

(4,18) = 34.53, p < 0.0001). Reaction times increased as the fixation letter position

increased from 1 to 5 in both visual fields (Fig. 4, Table 3).

None of the interactions were significant.

Table 2. Reaction times as a function of letter shape according to its position in a word (basic, initial, middle, and

final).

Letter Shape According to its Position in a Word Basic SD Initial SD Medial SD Final SD

468 105 473 101 499 108 496 112

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Figure 3. Reaction times as a function of letter shape according to its position in a word (basic, initial, middle, and

final). Note: Error bars represent standard error.

Table 3. Reaction times as a function of letter position (1, 2, 3, 4, and 5).

Letter Position Letter-1 SD Letter-2 SD Letter-3 SD Letter-4 SD Letter-5 SD

448 101 469 106 481 109 505 104 518 111

Figure 4. Reaction times as a function of letter position (1, 2, 3, 4, and 5). Note: Error bars represent standard

error.

The readability of connecting/un-connecting letters within un-connecting

letter strings was affected by visual eccentricity in Arabic. As expected,

recognition performance for letters was dependent on distance from fixation.

Reaction times for letters increased as a function of eccentricity. This pattern

Re

acti

on

Tim

e in

MS

Letter Shape according to its Position in Word

Re

acti

on

Tim

e in

MS

Letter Position

20

supports the visual acuity drop effect of letter recognition. In addition, the

readability of connecting/un-connecting letters was affected by visual field

presentation. As expected, recognition performance for letters presented in the right

visual field (RVF) was better than for letters presented in the left visual field

(LVF). This pattern supports the inter-hemispheric processing differentiation effect

of letter recognition. However, the effect of connecting/un-connecting letter

position within un-connecting letter strings by visual eccentricity in Arabic was

identical in RVF and LVF.

4. EXPERIMENT 2

Since a letter appears frequently within a multi-letter string, the present

experiment addressed the influence of the visual complexity of Arabic orthography

on letter identification OVP. Specifically, we were interested in how connecting (or

un-connecting) letters presented in all possible left or right visual field positions

within a multi-letter string of connecting letters would affect their identification.

Thus, the goal of the present experiment was to explore the OVP of connecting vs.

un-connecting letters within a multi-letter string of connecting letters in Arabic. An

initial fixation paradigm was used to present letters in the two visual fields (left,

right), in all letter fixation positions (1, 2, 3, 4, and 5), and according to their

position in the word (basic, initial, middle, and final). Participants were asked to

read (recognize) each presented letter. Participants’ performance was measured

according to accuracy rates and RTs for each letter condition. The main

experimental question was whether the OVP of Arabic letters within a multi-letter

string of connecting letters is dependent on their type (connecting, un-connecting),

their shape (basic, initial, middle, or final) and visual field presentation (left, right).

This is the first experiment to assess whether the OVP of Arabic letters within a

multi-letter string of connecting letters is modulated by the visual features of

connected and unconnected Arabic letters, their shape (basic, initial, middle, or

final), the visual field presentation (left, right), and the consequences for the higher

cognitive functioning needed for reading.

4.1. METHOD

4.1.1. Variables

The independent variables were letter type (connecting vs. un-connecting),

letter shape according to its position in the word (basic, initial, middle, and final),

21

visual field (left, right), and the initial fixation letter position (1, 2, 3, 4, and 5). The

dependent variables were accuracy rates and RTs for correct recognition. The

experimental matrix was a within-subjects quadric-factorial 2 × 4 × 2 × 5 design.

4.1.2. Participants

A total of 32 university students participated in this experiment (average age:

23.3, SD = 5, 10 males and 22 females). All were native Arabic speakers, from a

middle range of socio-economic status, right-handed, displayed normal or

corrected-to-normal vision in both eyes, and none had a history of neurological or

emotional disorders. In addition, no participant was formally diagnosed as having

reading impairments.

4.1.3. Stimuli

The same stimuli from Experiment 1 were used except that the connecting

letter (ل) was not used because the letters were in white 24 Simplified Arabic Fix

font embedded within a multi-letter string of 11 connecting " " ل on a (للللل ب للللل)

black background displayed on a PC screen.

4.1.4. Procedure

The procedure was the same as Experiment 4 except that stimuli were letters

within a multi-letter string of 11 connecting " " ل presented in all five (للللل ب للللل)

initial letter fixation positions for each visual field and the total number of trials

was 960.

4.2. RESULTS

Accuracy percentages exceeded 99% in all conditions; therefore, an accuracy

analysis was not conducted. The differences in reading latencies between the two

types of letters listed in the 2 lists according to their shape in the word (basic,

initial, middle, and final), visual field (left, right) and the initial fixation letter

position (1, 2, 3, 4, and 5) were analyzed with a repeated measures ANOVA.

The effect of letter type (connecting vs. un-connecting) was significant (F

(1,31) = 12.94, p < 0.005). Reaction times for the connecting letters (Mean = 490,

SD=105) were shorter than for the un-connecting letters (Mean = 508, SD = 107).

The effect of letter position (basic, initial, middle, and final) was significant

(F (3,29) = 4.64, p < 0.01). Reaction times for the medial position letters were

similar to the final position letters but longer than for the basic and initial position

letters (Fig. 5, Table 4).

22

The effect of visual field (left, right) was significant (F (1,31) = 4.56, p <

0.05). Reaction times for letters presented in the right visual field (Mean = 494, SD

= 105) were shorter than for letters presented in the left visual field (Mean = 504,

SD = 102).

The effect of letter fixation position (1, 2, 3, 4, and 5) was significant (F

(4,28) = 30.68, p < 0.0001). Reaction times for the letter increased as the fixation

letter position increased (Fig. 6, Table 5).

No interactions were significant.

Table 4. Reaction times as a function of letter shape according to its position in a word (basic, initial, middle, and final).

Letter Shape According to its Position in a Word

Basic SD Initial SD Medial SD Final SD

489 105 492 100 507 111 508 108

Figure 5. Reaction times as a function of letter shape according to its position in a word (basic, initial, middle, and

final). Note: Error bars represent standard error.

Re

acti

on

Tim

e in

MS

Letter Shape according to its Position in Word

23

Table 5. Reaction times as a function of letter position (1, 2, 3, 4, and 5).

Letter Position

Letter-1 SD Letter-2 SD Letter-3 SD Letter-4 SD Letter-5 SD

465 102 479 100 494 105 521 113 537 111

Figure 6. Reaction times as a function of letter position (1, 2, 3, 4, and 5). Note: Error bars represent standard

error.

The readability of connecting/un-connecting letters within connecting letter

strings was affected by visual eccentricity in Arabic. As expected, recognition

performance for letters was dependent on the distance from a fixation. Reaction

times for letters increased as a function of eccentricity. This pattern supports the

visual acuity drop effect of letter recognition. In addition, the readability of the

connecting/un-connecting letters was affected by visual field presentation. As

expected, recognition performance for letters presented in the right visual field

(RVF) was better than for letters presented in the left visual field (LVF). This

pattern supports the inter-hemispheric processing differentiation effect of letter

recognition. However, the effect of connecting/un-connecting letter position within

connecting letter strings by visual eccentricity in Arabic was identical in RVF and

LVF.

5. JOINT ANALYSIS

Re

acti

on

Tim

e in

MS

Letter Position

24

A joint analysis with the peripheral-unfixated letter presentation RTs of

Experiments 1and 2 was conducted. The within-subjects factor was letter

eccentricity (1, 2, 3, 4, and 5 letters to fixation) and the between-subjects factor

was letter string type (connecting, un-connecting) as manipulated in Experiments

1and 2, respectively. The mixed-design ANOVA revealed a significant effect of

letter eccentricity effect (F (1,73) = 33, p < 0.0001). Reaction times increased as

letter eccentricity increased. In addition, a letter string type effect was found (F

(2,73) = 4.9, p < 0.01). Reaction times for letters presented within un-connected

letter strings were shorter than letters presented within connecting letter strings.

The interaction between the factors was not significant (F (2,73) = 0.91, p = 0.401;

Fig. 7, Table 6).

Table 6. Reaction times for letter type (connecting, un-connecting) as a function of letter position in letter-string (1, 2, 3, 4, and 5) according to the letter string type (connecting, un-connecting). Note: Error bars represent

standard error.

Letter Position

Letter-1

SD Letter-

2 SD

Letter-3

SD Letter-

4 SD

Letter-5

SD

Letter

String

Type

Un-

connecting 448 101 469 106 481 109 505 104 518

111

Connecting 465 102 479 100 494 105 521 113 537 114

Figure 7. Reaction times for letter type (connecting, un-connecting) as a function of letter position in letter-string

(1, 2, 3, 4, and 5) according to the letter string type (connecting, un-connecting). Note: Error bars represent

standard error.

380390400410420430440450460470480490500510520530540550560

Letter-1 Letter-2 Letter-3 Letter-4 Letter-5

Re

acti

on

Tim

e in

MS

Letter Position

Un-connecting Connecting

25

6. GENERAL DISCUSSION

The critical finding from Experiments 1 and 2 was a symmetric drop-off in

average letter visibility as the initial fixation position moved from the center of the

stimulus to the periphery. These experiments replicated the well-known distance-

from-fixation effects for letter identification (e.g., Estes et al., 1976; Nazir,

Deutsch, Grainger, & Frost, 2000; Nazir et al., 1992). Recognition performance

was mostly a function of distance from fixation. The shape of the letter visibility

function varied substantially across the different fixation positions. There was one

pattern of letter visibility that emerged as fixation position varied. Fixations on the

central letter produced a visibility curve with a monotonic decline in performance

for letters further along the string. When the middle of an ten-letter string was

fixated upon, visibility dropped monotonically for letters further from fixation

(Stevens & Grainger, 2003).

In addition, results from Experiments 1 and 2 appear to conform to prior

reports of higher levels of letter visibility in the right visual field (Bouma, 1973;

Kajii & Osaka, 2000; Nazir et al., 1992). Having the Arabic letters presented

within a long string (11 letters) induced a specific processing bias that gave rise to

superior visibility for letters presented in the right visual field. However, the effect

of connecting/un-connecting letter position by visual eccentricity in Arabic was

identical in RVF and LVF.

It is interesting to note that Nazir et al. (2000), in their study of Hebrew (a

language read from right to left), found that letters to the right of a fixation were

identified better than letters to the left of a fixation.

Results from the present study replicated the standard finding of a drop in

performance with two flanking stimuli. The presence and the type of a letter string,

affect letter identification. A letter presented within a connecting letter string

(connecting flankers) showed even more interference than a letter presented within

an un-connecting letter string (un-connecting flankers). This is in line with visual

attentional accounts of crowding (Strasburger et al., 1991; Intriligator & Cavanagh,

2001; Strasburger, 2005) by which attentional deployment determines the extent of

the crowding zone (Marzouki et al., 2013). The the type of flankers, as in the un-

connecting letter string presentation conditions, would facilitate a focus of attention

on the target letter since the inter-letter spacing enables better visual segregation

(i.e., the target letter pops out). This is similar to the notion that different colored

targets are thought to help focus attention (Scolari et al. 2007, Whitney & Levi,

26

2011). However, the connecting letter string presentation has excessive feature

integration (perceptual grouping) that decreases the target letter’s capacity to resist

flanker interference (Desimone & Duncan, 1995). These findings are in line with

prior studies showing that attracting visual attention to the target location can

reduce crowding (Yeshurun & Rashal, 2010). One way to accommodate these

influences of visual attention with an account of crowding in Arabic is via the type

of letter string (connecting, un-connecting).

Since, sensitivity to statistical regularities of visual orthographic input

emerges as a product of learning to read, effects of letter frequency were also

observed in the performance of skilled readers on a low-level task. However, this

does not explicitly activate lexical representations such as visual letter recognition

or identification; this does assume that these tasks tap into the written word

recognition system (Pitchford & Lefgeway, 2008). Since using letter strings instead

of real words in tasks investigating letter identification minimizes the effects of

top-down processes, the advantage of recognizing connecting Arabic letter types

compared with un-connecting letter types, would suggest that this effect operates

at, or modulates, a relatively early stage of visual orthographic processing (e.g.,

abstract letter encoding).

In sum, the present study investigated the influence of the presence and type

of flanking elements, as well as target letter eccentricity, in a letter-in-string

identification task. Results revealed a standard crowding effect in both connecting

and un-connecting letter-string presentation conditions, with target letter

identification being more difficult when target letters were surrounded by

connecting flankers compared with a un-connecting flanker condition. Most

importantly, connecting flankers caused a further decrement in performance in

contradiction to Abdelhadi, Ibrahim, & Eviatar's (2011) findings that vowel

detection in Arabic was better for letter strings containing connected letters than for

those containing unconnected letters. This could be explained by the difference

between the vowel detection task used by Abdelhadi, Ibrahim, & Eviatar (2011)

and our letter detection task embedded in a letter string. Since in Arabic vowels

appear above or below the letters, vowel detection is facilitated in connected letter

string, while letter detection is inhibited when embedded in a connected letter

string compared with unconnecting letter string as in the present study. Finally, the

type of flanking stimulus (connecting, un-connecting) and the visual field (left,

right) modulated flanker interference. Reading rates were worse for letter stimuli

that had been embedded within a connecting letter string compared to an un-

27

connecting letter string; this is highlighted by inter-letter spacing relative to the

letter’s eccentric placement across the letter string and visual field. We argue that

the most parsimonious account of the present findings is related to visual Arabic

letter connectedness, visual acuity, and crowding (flanker interference).

These results indicate that it might be possible to standardize reading rates

across the visual field by compensating for reduced acuity, elevated crowding, and

eccentric position to better equate the visibility of letters within words.

Additionally, we now have an empirically determined set of letter visibility

measures as a function of letter type, letter string type, and possible fixation

position in Arabic. These letter visibility results, in conjunction with various

measures of lexical constraint, are useful for attempting to predict performance

obtained with Arabic word stimuli while assessing the OVP and length effects.

The results of this study have important implications for current theories on

encoding letter identity within written word recognition. Several specific, yet

contrasting, models of letter position encoding have been proposed in recent years

(see Davis, 2006; Schoonbaert & Grainger, 2004, for a detailed review). In some

respects, our findings are most consistent with serial models of letter position

encoding (e.g. Whitney, 2001). However, to be considered suitable for Arabic,

models of letter recognition should take into account the present findings. This may

involve modifying models such that the models incorporate: (i) the type of letters

(connecting, un-connecting) by which processing Arabic orthography would

benefit identification of connecting letters, (ii) the shape of letters (basic, initial,

medial, and final), and (iii) the type of letter string.

7. SUMMARY AND CONCLUSIONS

The visual letter recognition is influenced by: (i) the letters' type (connecting,

un-connecting), as connecting letters are easier to recognize than in-connecting

letters; and (ii) letters' shape (basic, initial, medial, final), as medial and final are

harder to recognize than basic and initial letter shapes, (iii) letter string's type, as

reading rates were longer for letter stimuli that have been embedded within a

connecting letter string compared to an un-connecting letter string with inter-letter

spacing, (iv) visual field, as reading rates were longer for letter stimuli that have

been presented in LVF compared to RVF, (v) eccentricity, as letter reading rates

were correlated with its eccentric placement across the letter string.

The present study revealed a standard crowding effect in both connecting and

un-connecting letter strings presentation conditions, with target letter identification

28

being harder when target letters were surrounded by connecting flankers compared

with the un-connecting flanker condition. Most important, however, is that the

connecting flankers caused a further decrement in performance. Finally, flanker

interference was modulated by both the type of flanking stimulus (connecting, un-

connecting) and the visual field (left, right). Reading rates are longer for letter

stimuli that have been embedded within a connecting letter string compared to an

un-connecting letter string with inter-letter spacing and relative to its eccentric

placement across the letter string and the visual field.

We argue that the most parsimonious account of the complete set of findings

is in terms of visual Arabic letters connectedness, visual acuity, plus the crowding

(flanker interference). Practically, these results indicate that it might be possible to

standardize reading rates across the visual field by compensating for reduced

acuity, elevated crowding, and eccentric position to better equate the visibility of

letters within words. Theoretically, the results of this study have important

implications for current theories on encoding letter identity within written word

recognition. However, since there are universal processes in reading and writing-

system specific processes (Perfetti, Cao, & Booth, 2013), in the letter level our

findings are most consistent with serial models of letter position encoding (e.g.

Whitney, 2001) while in the word level our findings are most consistent with the

dual route model.

ACKNOWLEDGMENT

This work was carried out under the supervision of Prof. Michal Lavidor,

Department of Psychology, Bar-Ilan University. I would especially like to

thank my supervisor Prof. Michal Lavidor, whose insights and guidance

continually challenged me throughout this experience. I wish to thank her for all

the time and effort she invested in me and for all the freedom she gave me to

pursue my ideas throughout this gratifying process.

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