Age, iconic storage, and visual information processing

.TOURNAL

Age,

“F

EXPERIMENTAL

lconic

CHILD

Storage,

I’HTCHOLOGY

and

Visual

13,

165-170

Information

(1972)

Processingl>”

Second, fourth, and sislh grade stutlents and college adults identified simple stimuli presented tschistoscopirnll~~. A stimulus was followed b? either a homogeneous whitr field or a patterned masking stimulus. The I&tcrncd mask wan assumed to stop procrssing of the stimulus information rctaincd in iconic storage. while the white field would simply degrade thr stimulus. All groups performed equally well when the whit,e field followed the stimulus, but the sixth-graders and adults were more accurate than the second and fourth graders when t,he pnttcrned mask was used. This outcome is consistrnt with t,he notion that young children’s iconic storage is longer than that of older children and adults but that young children process the information in iconic storage relatively slowly.

Current conceptions of human perceptual processes (see Haber, 1969; Neisser, 1967) suggest that the information contained in a brief visual stimulus is not static but is represented in different forms at different times after the offset of the stimulus. Init,ially, a great deal of the inforshort-lived storage system known mation is retained in a high-capacity, as the “icon” (Neiseer, 1967). Since the icon decays rapidly (it is usually gone in less than 1 set), it seldom serves as the basis for overt respondprocesses transfer a smaller, more manageable ing. Instead, “encoding” portion of the information from the fading icon to another memory system-known as ‘Lprinlary” memory (Laugh & Norman, 1965) or simply STM (“short-term memory”)-which is more resistant to decay but of considerably more limited capacity. The STM, which can bc reinstated nnd strengthened by rehearsal processes, endures long enough to provide information for subsequent decision-making and responding. A great deal of research with adult S’s has dealt with this type of informat’ion-processing system, but few studies have investigated the characteristics of the system RR it, exists in children. The developmental ’ This rese:~wh was suppori~i 1)~ tl1(3 National Science Foundation University Scknw Drvelopmcnt Program. Grant GLJ-1595. We are grateful for the cooperation and nssistancc of the Austin, TX. Independent School District. and the principal ;urd staff of 8ummitt, Elemcntarv School. “ Itc~~u(~sts for wprinta slro111tl 1~ writ t,o Kent Gummerman, Depart,ment of Psq-teleology, Meets Hall 211, The University of Texas at Austin, Austin, TX 78712. 165 @ 1972 by

Academic

Press,

Inc.

work that has been done suggests that t’he early stages of children’s information processing differ from adults’ in at least 2 ways: t’hc icon seems to last longer in children than in adults, and children do not process the icon’s information as rapidly as adults. Evidence for the difference in icon duration stems from the findings of Pollaek, Ptashne, and Carter (1969)) who measured the length of the dark interval between 2 flashes of light that was just sufficient to allow tletcction of the interval. The size of this dark-interval threshold was negatively relatetl to chronological age, suggesting that stimulus persistence (i.e., the duration of the icon) declined with ngc. Spitz and Thor (1968) and Liss and Haith (1970) presentetl data to suggest that the speed of processing (encoding) increases with mental age. Since their tasks involved processing shape information under backward masking c,onditions (Kahncman, 1968) designed to holcl icon duration constant for all subjects (Lisa. 1968; Scharf & Lefton, 1970; Spencer, 1969; Spencer k Shuntich, 1970), the observed poor performance by Ss of low mental age was indicative of their slow and inefficient processing. At present, age changes in icon duration have not been demonstrat#ed in a forced-choice form identification task; furthermore, icon duration and processing speed have not been explored simult,aneously within the. same set of Ss. The experiment, reported here was intended to provide data of this type. Children and adults identified simple shapes in 2 backward masking conditions. On half the trials, the stimulus was immediately followed by a homogeneous white masking field (condition WM). This type of mask was assumed to reduce figure-ground contrast (see Kahneman, 1968) but to leave icon duration unaffected and free to vary.” On t.he remaining trials, a patterned noise mask followed the stimulus (condition PM1 ; we assumed, as did Spitz and Thor (1968) and Liss and Haith (1970), that t’he appearance of such a mask would immediately interrupt processing of the icon’s information so that icon duration was constant for all Ss. Since performance in condition PAflI should have been determined solely by processing speed, we anticillatetl an increase in performance with age for PM. In condition \$W, accuracy TVOU~C~ also depend 011 processing speed, but it should also reflect tJ)c different amounts of processing time available (i.e., differetlt icon durations) for Ss of different ages. Specifically, w’p expected to fin(l much “Liss and HaitII (1970) nscd :I patterned mask precctli>lg thr t hr Sam? function. This tylw of “fonvard mask” does seem to hp it apparrntly does not. affect iron duration Ihe way a patterned IIOI~S (Rcharf & Lc>fton. 1970) ; llowwrr. IVP c.hose t,o use a white tllct stimulns instead. bC(‘ause the nature of its interaction with the c~stcnsivelg explored and seems to hr more straightfonva.rd.

stimulus to serve appropriate, since “bwkwartl ma&” mark follolving stimulu* has bec,n

VISUAL

INFORMATION

PROCESSIXG

167

less improvement with age in WM than in PM because the slow processing of younger Ss would be offset to some dcgrec by their greater icon duration. METHOD

S&jects. The Ss were 36 children from the second, fourth, and sixth grades of an Austin, TX, elementary school and 12 adults from introduct.ory psychology classes at the University of Texas. There were 6 males and 6 females in each age group; all had normal vision and none had any previous experience with t,achistoscopic experiments. No estimates of MA ,or cognitive maturity were available for the children other than the knowledge that they were functioning normally in a middle- or upper-middle class public school. Apparatus and materials. Stimuli were presented in a a-field mirror tachist’oscope (Scientific Prototype) at a viewing distance of 80.5 cm. The luminance of the white portions of all displays was about 23 ft-L. Two black-on-white stimuli were made by blackening 5 cells in 3 X 3 square matrices that subtended 40 min visual angle on a side. The matrices were outlined in black on white card stock. The blackened cells formed a block capital T rotated 90” either to the left or to the right. A patterned mask was constructed in a manner similar to the test stimuli-cells in a 5 X 5 matrix (67 min on a side) were blackened randomly, with the restriction that’ there be the same amount of overlap with each of the 2 test items. On trials when the patterned mask did not follow t.he test items, a blank white card was illuminated in the masking field. The preexposure field was dark ; a central fixation point was provided by an electroluminescent panel placed behind a pin hole in the center of the masking st.imulus. Test stimulus durations were selected in pilot work which allowed adults SO-SO% accuracy. For the pattern mask condit,ion (PM), this duration was 80 msec; for the white mask condition (WM), 10 msec. Masking field exposure duration was 5 sec. The S’s triggered the onset of the test item with a hand-held switch; the masking stimulus followed immediately. Procedure. Each S participated in 2 individual sessionson successive days. At the beginning of the first session, the S was acquainted with the tachistoscope and materials. The names ‘(right” and “left” were used to indicate whether the perpendicular bar of the T appeared on the right or left. The E played a short game with each child at the beginning of the first session to insure that be could reliably differentiate “right” from “left.” During each session a block of 14 trials was

168

CiUMMERMAiV

AND

GRAY

presented for each of the 2 mask conditions. For half of each group, condition PM was run first; for the other half, condition WM was first. Stimulus sequences were determined randomly, with the restriction that the 2 stimuli appear equally often in each 14-trial block. The S was instructed to focus on the fixation point, to begin each trial when ready, and to make a verbal report of “left” or “right” when the tachistoscope was dark again at the end of each trial. AI l)rief rest was taken between conclitions. Iu summary, thcrr were 3 between-group factors in the design: ,4ge, Sex, and Presentation Sequence. Mask Condition (\VRil X-S PM) and Days were within-& factors. There were 14 2-alternative forced-choice trials in each mask condition on each of 2 successive days, for a total of 56 trials 1)er S. Data reliability was assessed with a 5-way miseddesign analysis of T-ariancc. REST’LTS

AKD

DISCUSSION

An expected result was that experience with the task was helpful: performance was better on the second day 182.1%) than on the first (76.5%)) (F (I ,32) = 14.8, p < .Ol ), but this factor did not interact with any others. As Table 1 shows, overall performance was influenced by grade (F 13,32) = 4.3, p < .02). Surprisingly, sixth graders were more accurate overall than any other age group. Performance was, in general, better in W’?\1than in PM (86.5c/u 17s73.091) iF(1,32) = 29.8, p < .Ol), though the use of different. exposure durations for the two conditions makes this result unintcrcsting. Pcx of subject and the order of presentation of mask conditions (lid not affect l)crformance in any way. The outcome of interest is the reliable (F (3,321 = 3.6, p < ,051 interaction between grade and mask condition (see Table 1 ) This interaction was cxplorecl in greater detail with post-hoc pairwisc qjccific comparisons; Table 2 givca the F ratios that resulted from this analysis. All children l>erformed at least as well as adults when the l~on~oge~~eo~~s

Grade College

Average over grade

s:< !)

sti.5

so, 7 s” :;

7:3 0 7!). s

TABLI!: 2 P.WZV~ISI~, POST HOC SPPXIYIC COMPAKIWNS IN GR,IDIC z TYIV: OF IVI.ISS INTI~XICTION

F-RATIOS FROM ALL

Conditions

OF ME.IN~S

4-PM

6-m

A-W-L1

2.1

21’). 4” lTO.@

213

2-Plf 4-PM B-PM A-PM “-WM 4-WM 6-WRI

4”

17:: 661 0. I 4.P 0.2 0 h 42.

I ‘I

(1 /I < .OOl. *p < .05. “p < .Ol.

white mask followed the stimulus. In fact, sixth graders performed significantly better than adults in condition WM. Thus, when the icon is not curtailed, children seem able to extract as much or more information from the stimulus as adults. When the patterned mask was used to keep icon duration constant, however, second and fourth graders performed significantly poorer than the sixth graders and adults. These findings support our original hypotheses about icon duration and processing speed. The increase in accuracy with age in the situation designed to limit the icon’s duration to the time that the distal stimulus was exposed (condition PM) suggeststhat young children do not transfer information from iconic storage to STM as rapidly as older children and adults. This same slow processing must hinder the younger children in condition WM as well, but the deficit appears to he compensated for by the longer-lasting icon available to young children in WAI. The sixth graders’ overall level of performance was unexpected, since accuracy in this type of task is t,ypically a monotonic funrtion of age. The cause of the sixth graders’ superiority is not known. The present task is not radically different from those used by earlier investigations, so one might be led to suspect peculiarities in the samples of sixth graders and adult Ss. Considering the present data in isolation, however, the sixth graders’ scores can be explained by assuming that these young Ss enjoy not only adult-like processing speed but also a relatively longlasting icon. These inferences about icon duration agree with Pollack et al.% interpretations, and the different processing speedsreflected in the PM scores support the findings of Spitz and Thor (1968) and Liss and Haith (1970).

Furthermore, the relationship between processing speed and age is clearly nonlinear: fourth graders performed like children, and sixth graders performed like adults. This discontinuity corresponds to Liss and Haith’s (1970) report that lo-year-olds’ processing speed resembled that of adults more closely than that of 5-year-olds. It is noteworthy that Piaget (1967) places the transition from concrete to formal operational stages of cognitive development, at approximately 11 to 12 years. Assuming that cognit’ive maturity might be a determinant of perceptual processing strategies, this shift in cognit,ive functioning may have contributed to the differences in encoding observed at different, ages. REFERENCES HABER,

It.

York: KAHNEMAN,

logical

approaches to visual perception. New Holt, Rinehart and Winston, 1969. D. Method, findings, and theory in studies of visual masking. PsychoX.

(Ed.)

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Information-processing

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LISS, P. Does backward ception LISS.

und

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Psychophysics,

by visual noise stop stimulus

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processing?

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P. H., & HAITH, M. M. The speed of visual processing in children and adults: Effects of backward and forward masking. Perception and Psychophysics, 1970, 8, 39G398.

NISISSER, U. Cognitive psychology. New York: Appleton-Century-Crofts, 1967. PIAGET, J. Six psychological studies (trans.). New York: Random House, 1967. POLLACK, R. H., PTASHNE, R.. I., 8: CARTER, D. J. The effects of age and intelligence on the dark-interval threshold. Perception and Psychophysics, 1969, 6, 50-52. SCHARF, B., & LEFTON, L. A. Backward and forward masking as a function of stimulus and task parameters. Jonrnal of Experimental Psychology, 1970, 84, 331-338.

SP~XCER, T. J. Some effects of different masking stimuli on iconic storage. Journal of Expelimental Psychology, 1969, 81, 132-140. SPENCER, T. J., & SHUNTICH, R. Evidence for an interruption theory of backward masking. Journal of Experimental Psychology, 1970, 85, 398-203. SPITZ, H. H., & THOR, D. H. Visual backward masking in retardates and normals. Perception

and

Psychophysics,

1968,

4, 245-246. memory.

WAUGH, N. C., & NORMAN, D. A. Primary 72, 89-104.

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1965,