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Fast development of iconic memory: Infants’ capacity matches adults’
Erik Blaser, PhD. & Zsuzsa Kaldy, PhD.University of Massachusetts Boston
Department of Psychology
MotivationIconic memory is the first visual information buffer, yet
its capacity has never been measured in infants.
GoalDevise a partial report iconic memory paradigm that can be applied both to infants and adults. Compare their capacities.
Iconic memory is the high capacity, short-lived initial store of visual information (Sperling, 1960). Iconic memory has
never been studied in infants.
Here we apply a novel partial report procedure to both infants and adults.
‘Whole report’ tests of ‘very short term memory’ (<300 ms retention) are remarkably low, e.g. just one item for
6.5 month olds (Oakes, Ross-Sheehy, & Luck, 2006).
‘Partial report’ was the key to measuring iconic memory (Sperling, 1960).
Introduction
fixation3.0 seconds
objects are presented1.0 second
a ‘critical pair’ disappears. 500 ms
‘Decoy’ and ‘Target’ reappear2 seconds
presentation partial report cue 2AFC memory test
Red dot shows gaze location,
diameter shows duration
The Target changes color.
The Decoy reappears unchanged
A partial report, 2AFC test of iconic memory for infants and adults
This offset itself acts as a post-cue
Decoy TargetSet Size 8
Rapid developmentRecent fMRI studies in adults attribute iconic memory to persistent activation in higher-order visual areas such as the occipito-temporal cortex, particularly the lateral-occipital complex (LOC; Ruff, Kristjánsson, & Driver, 2007; Wong, Aldcroft, Large, Culham, & Vilis, 2009). Indeed, the occipital lobe is the part of the cortex that matures earliest (Huttenlocher, 1990), and the area corresponding to LOC in adults has been shown to be active at 6.5 months of age (Wilcox et al., 2009).
LO
V1
V1
V2
V2V3
V3
V4
MT+
LO
V1V2V3
V4
V1V2
V3
MT+
Vanish > MaskA
Vanish > MaskLeft Left RightRight
25.0025.00
6.506.50t(8358)t(8358)
-11p < 8.4 x10-11p < 8.4 x10p(Bonf) < 0.000p(Bonf) < 0.000
10.0010.00
5.005.00t(8358)
p < 5.8x10p(Bonf) < 0.009
-7t(8358)
-7p < 5.8x10p(Bonf) < 0.009
Blaser, E., & Kaldy, Z. (2010). Psychological Science, 21, 1643-1645.
Cowan, N. (2001). Behavioral & Brain Sciences, 24, 87-185.
Huttenlocher, P.R. (1990). Neuropsychologia, 28, 517-527.
Oakes, L.M., Ross-Sheehy, S., & Luck, S.J. (2006). Psychological Science,17, 781-7.
Ruff, C.C., Kristjánsson, Á., & Driver, J. (2007). Psychological Science, 18, 901-909.
Sperling, G. (1960). Psychological Monographs: General and Applied, 74, 1-29.
Wilcox, T., Bortfeld, H., Woods, R., Wruck, E., Armstrong, J., & Boas, D. (2009). Neuropsychologia, 47, 657-662.
Wong, Y.J., Aldcroft, A.J., Large, M.E., Culham, J.C., & Vilis, T. (2009). J Neurophys. 102, 3461-3468.
References
This research was supported by National Institutes of Health Grant 2R15EY017985 awarded to the authors
Participants: A total of 62 infants, ~12 per set size, aged 5;00-6;30. 5 ‘Expert’ adults were run, and 12 ‘Naive’/‘Instructed’. Materials: A Tobii T120 eye tracker was used for display and recording. Procedure: Infants were presented with two blocks of 18 test trials. Depending on block, a set of 2, 4, 6, 8, or 10 identically-shaped, but differently-colored items appeared, spaced symmetrically around fixation (adults saw all set sizes). After a 1 sec exposure, a randomly chosen pair of (neighboring) items disappeared. After a 500 ms delay the two items reappeared, with one changed to a new color (Target) and the other unchanged (Decoy). The sudden offset of the pair itself was the partial report post-cue. Since the pair was chosen randomly, any differential treatment of Target vs. Decoy is evidence that information about the items was in memory prior to offset.
Percent correct should be maximal when set size is below capacity, and drop as
capacity is exceeded. This breakpoint is used to estimate capacity (Cowan, 2001).
Our results show nearly identical (5-6 item) iconic memory capacities for 6-month-old infants, instructed adults and expert adults.
Iconic memory, 6 month olds Infant vs. Adult capacity
40
50
60
70
80
90
100
2 4 6 8 1050
55
60
65
70
2 4 6 8 10
Attention grabber (8.5 s)
Presentation (1 s)
Partial report offset post-cue
(500 ms)
Preferential looking memory test (2.5 s)
Fixation (1 s)
Set size
Perc
ent c
orre
ct ***
n.s.
n.s.
**
Preference for Changed object
A trial-by-trial, head-to-head 2AFC comparison
between Target and Decoy. Trials where the Target is
‘preferred’ (fixated longer) are coded as correct.
Capacity estimates shown by red arrows.Expert: 5.75 items; Instructed: 5; Infant: 5; Naive: 2
Set size
Perc
ent c
orre
ct
Preference for Changed object
Blaser & Kaldy, (2010). Psychological Science
Tobii T120
Naive adults had no task knowledge, much
as the infants. Instructed adults were fully
briefed about the experiment and asked to fixate the Changed
item as quickly and for as long as possible. Expert adults were
similarly instructed, and had had previous
experience in visual psychophysics experiments.
Results
We applied a novel partial report test to compare infants’ iconic memory capacity to that of adults.
Our results show a five item iconic memory capacity in 6-month olds.
Infant iconic memory capacity matches adults’ (~5-6 items)(...and, provocatively, exceeds that of naive undergraduates...)
Infants’ and adults’ match in capacity points to particularly rapid development.
Conclusions
InfantsNaive
Expert
Instructed
Replication of set size 4 with independent infant group