Detection of stimulus organization: Evidence of intelligence-related differences

INTELLIGENCE 14, 435-447 (1990)

Detection of Stimulus Organization" Evidence of Intelligence-Related Differences SAL A . SORACI, JR. M I C H A E L T . CARLIN CHARLES W . DECKNER ALFRED A . BAUME1STER

Vanderbilt University

Utilizing checkerboard-like stimulus patterns varying with respect to symmetry and number of adjacencies, the effects of stimulus structure on the performances of mentally retarded and nonretarded subjects on a rapid-presentation match-to-sample task were examined. The disparity between target and distractor stimuli was manipulated across high, low, and moderate levels of stimulus organization. Consistent with previous findings (i.e., Caruso & Detterman, 1983), detection rates for the two groups were equivalent at both high and low levels of distractor organization. Of particular importance, however, was that intelligence-related performance differences were evident only with distractors of intermediate organization. The influence of stimulus structure on stimulus detectability, and the implications of these findings for explaining intelligence-related differences across a wide range of tasks are discussed.

T h e influence o f stimulus organization is a central issue in discussions o f p e r c e p tual and e n c o d i n g processes. Uttal (1983) has e m p h a s i z e d the importance o f stimulus attributes in visual f o r m detection. W h e n stimulus organization parameters are varied, stimulus detection, recognition, and discrimination are a function o f the d e g r e e to w h i c h the organization o f a particular stimulus approximates vertical symmetry. This relationship has been found not only with adults (Alexander & Carey, 1968; H o w e , 1980; P a l m e r & H e m e n w a y , 1978), but also parallels a g e - c o r r e l a t e d differences (Bornstein & Stiles-Davis, 1984; C h i p m a n & M e n d e l s o n , 1979). T h e basic premise is that the higher-order organization e m -

This research was supported by the National Institute of Child Health and Human Development Research Program Project Grant #HD 15051, NICHD Grant #HD 23682, and NICHD Grant # I K04HD00921-01. Portions of this paper were presented at the Gatlinburg Conference on Mental Retardation, Gatlinburg, TN, March 1989, and the 30th Annual Meeting of the Psychonomic Society, Atlanta, GA, November 1989. Correspondence and requests for reprints should be sent to S.A. Soraci, Peabody College, Box 154, Vanderbilt University, Nashville, TN 37203. 435

436

SORACI, CARLIN, DECKNER, AND BAUMEISTER

bodied in symmetrical stimuli enhances the encodability and hence subsequent discrimination of a given stimulus. Although research has demonstrated differences in the detectability of various degrees of stimulus organization, only one study (Caruso & Detterman, 1983) has attempted to manipulate such organizational indices in examining intelligence-related differences in encoding. Caruso and Detterman (1983) used checkerboard-like patterns in a four-choice match-to-sample task. The organizational structures of the standard, or target stimulus, and the surrounding three distractor stimuli were varied. The results indicated that, although mentally retarded individuals were slower and made more errors, mentally retarded and nonretarded subjects were equally influenced by the structural characteristics of the stimuli. Several factors limit the conclusions that can be drawn from the findings of Caruso and Detterman. First, the target stimulus remained visible to the subject while a response was being made; that is, inspection time was unlimited. Since the memory demands of the task were minimal, it is not clear that encoding processes per se were primarily involved. Second, distractor effects were assessed by comparing the structure of the target stimulus to the "mean" structure of the three distractor stimuli on each trial. Thus, Caruso and Detterman were not able to examine stimulus disparity effects in a pairwise comparison format due to their use of three heterogeneous distractor stimuli on each trial. Such interactive effects involving the influence of the distractor (i.e., "surround"; cf. Garner, 1974; Sekuler and Blake, 1985) on target detection are critical in tasks involving two-choice discriminations (Gibson, 1979; Uttal, 1983). Finally, and perhaps most important for the purposes of the present paper, Caruso and Detterman examined correlations between decision times and stimulus structure variables across a continuum of either highly organized or random sets. Intermediate levels of stimulus structure did not comprise a discrete factor in their study. For the previously mentioned reasons, it is important to explore the relationship between stimulus organization and stimulus detection in mentally retarded and nonretarded individuals using (a) a rapid-presentation format, (b) multiple, discrete levels of stimulus organization, and (c) interstimulus comparison data. The present study was designed to examine detection differences between mentally retarded and nonretarded individuals via the presentation of high, intermediate, and low stimulus organizations of both target and distractor stimuli. In the present experiment, target stimuli were exposed for brief durations (less than 150 ms) that permitted only central scanning of the target stimulus. Central scanning implies that only a single visual fixation of the stimulus would be possible. In addition, a two-choice match-to-sample task was employed to allow direct examination of the effects of distractor structure on performance. As Dinsmoor (1985) has suggested, the amount of physical disparity between two comparison stimuli is a critical factor in the relative discriminability of a pair of stimuli. The utilization of brief exposure durations and the inclusion of a l-s

DETECTION OF STIMULUSORGANIZATION

437

interstimulus interval between target removal and presentation of the targetdistractor choice was designed to impose a memory demand. Using more global stimulus arrays in tasks such as oddity, research conducted by the present investigators (Soraci, Barlean, Haenlein, & Baumeister, 1986; Soraci et al., 1987) has demonstrated intelligence-related differences at moderate levels of stimulus organization. Thus, although the general hypothesis was that the performances of groups differing in intelligence would replicate Caruso and Detterman's findings at the high and low levels of stimulus organization, we also were interested in examining possible group differences at moderate levels of organization in a more stimulus-specific context.

METHOD Subjects Thirty students from the Nashville Metropolitan School System participated in the study. Group 1 consisted of 16 mildly mentally retarded students from special education classes. The mean chronological age (CA) for this group was 16.5 years with a standard deviation (SD) of 1.5 years. The mean IQ for the mentally retarded subjects was 66.1 with an SD of 5.51. Group 2, CA-matched control subjects, consisted of 14 students from regular education classes in the same schools. The mean CA for this group was 15.6 years with an SD of 2.31. All subjects who participated in the study were assessed as having normal or corrected-to-normal vision. In addition, subjects received $10.00 as compensation for their participation.

Experimental Design A 2(Group) by 3(Target Structure) by 3(Distractor Structure) group design was implemented with Target Structure (high, moderate, or low) and Distractor Structure (high, moderate, or low) as within-subjects factors. Dependent measures consisted of the mean percent correct recognitions and mean reaction times for each subject in each experimental condition.

Stimuli Stimuli were twelve 4 x 4 rectangular matrices similar to those used by Caruso and Detterman (1983). Each stimulus measured 30 mm x 36 mm, with each cell 6.5 mm x 8.0 ram. These stimuli were quantifiable on each of three stimulus structure continua: symmetry, number of adjacencies, and number of cells filled. There were four possible axes of symmetry: horizontal, vertical, left diagonal, and right diagonal. Similarly, there were two types of adjacencies: rectilinear and diagonalinear. Rectilinear adjacencies were defined by two or more filled cells sharing a common side. Diagonalinear adjacencies were defined by two or more filled cells sharing a common comer. Finally, three levels of filled cells were employed: 4, 6, and 8.

438

SORACI, CARLIN, DECKNER, AND BAUMEISTER

A stimulus structure rating was assigned to each stimulus based upon a chunking (i.e., adjacency) score and whether the stimulus was symmetrical or asymmetrical. The following formula was used to calculate the chunking score (CS) for each stimulus, CS = [(#rectilinear adjacencies) + V2 (#diagonalinear adjacencies)/#cells filled]. In addition, symmetrical stimuli were assigned a value of one, and asymmetrical stimuli a value of zero. The stimulus structure rating for each stimulus, therefore, was equal to the sum of the chunking score and the symmetry value. Stimulus structure ratings for the stimuli in each of the three structural conditions are displayed in Table 1. Stimuli which were symmetrical and contained a high number of adjacencies per cells filled were classified as highly structured (HH). Three of the 12 stimuli, one at each level of filled cells, were of this type. Column A in Figure 1 contains the 3 stimuli classified as high in structure. Moderately structured stimuli were either symmetrical and contained a low number of adjacencies per cells filled (HL), or were nonsymmetrical and contained a high number of adjacencies per cells filled (LH). These two types of mixed organization were classified together as moderate structure. Three examples of each of the two types of moderate structure, one at each level of filled cells, were used in the study. Column B 1 in Figure 1 contains the 3 stimuli which were symmetrical and contained a low number of adjacencies per cells filled (HL), and column B2 contains the 3 stimuli which were nonsymmetrical and contained a high number of adjacencies per cells filled (LH). Finally, Column C in Figure 1 contains stimuli which were nonsymmetrical and contained a low number of adjacencies per cells filled and were classified as low in structure (LL). Apparatus

A Hewlett-Packard Vectra computer with Color Graphics Adaptor and touchscreen was used for stimulus presentation and response recording. Stimuli were presented on the CGA computer monitor positioned at eye level and within easy reach (approximately 55 cm) of the subject. Subject responses were automatically recorded by the computer for analysis. For each matching trial, the computer

TABLE 1 Chunking Scores and Stimulus Structure Ratings for the Three Stimuli in Each Structural Category a Stimulus Structure

Chunking Scores

Structural Rating

High (HH) Moderate 1 (HL) Moderate 2 (LH) Low (LL)

1.25, 1.00, 1.31 0.00, 0.50, 0.75 0.63, 0.75, 1.25 0.00, 0.25, 0.50

2.25, 2.00, 2.31 1.00, 1.50, 1.75 0.63, 0.75, 1.25 0.00, 0.25, 0.50

aThe moderate structure condition was divided into two groups for this analysis to represent the two types of mixed structure.

439

DETECTION OF STIMULUS ORGANIZATION

A

BI

B2

C

FIG. 1. Stimuli used in the study: (A) High Structure, high symmetry-high adjacency, (BI) Moderate Structure, high symmetry-low adjacency, (B2) Moderate Structure, low symmetry-high adjacency, (C) Low Structure, low symmetry-low adjacency.

recorded which of the 12 stimuli were compared and the correctness of the subject's decision. The subject's reaction time (RT) from onset of the twostimulus array until a decision had been made also was recorded.

Experimental Procedure Pretesting of mentally retarded and nonretarded subjects was conducted to determine exposure durations (from onset of the target stimulus to mask onset) which would allow only central processing of the target stimulus. Central processing implies that only a single visual fixation of the stimulus would be possible. Scanning processes, therefore, would operate on a short-duration sensory afterimage (Sperling, 1960). Generally, it is believed that stimulus exposures of 5 to 150 ms are in the central processing range. In the present study, exposures at which mean percent correct recognitions for each pretest group were approximately 75% were used. This criterion served to equate groups on overall task difficulty and to eliminate floor and ceiling effects. Based on this criterion, stimulus exposure durations used for the mentally retarded and nonretarded groups were 100 ms and 50 ms, respectively. These stimulus exposure differences were in agreement with the earlier findings of Nettlebeck and Lally (1979) on inspection time. Their results indicated that persons with mental retardation required approximately twice as much time to accumulate comparable

440

SORACI, CARLIN, DECKNER, AND BAUMEISTER

amounts of stimulus information for processing as did nonretarded individuals. Further, Caruso (1985) has demonstrated that the memory deficit of mentally retarded individuals may be independent of this stimulus identification deficit. A rapid-presentation two-choice match-to-sample task was employed. Each subject was given a brief verbal description of the experimental task. Subjects were informed that a checkerboard pattern, the target stimulus, would flash on the computer monitor and then disappear. Following a 1-s interval, two checkerboard patterns would appear. Subjects were instructed to touch the stimulus matching the previously displayed target stimulus. If unsure of the correct choice, subjects were instructed to guess. A set of 10 practice trials was implemented at 500-ms exposures to familiarize subjects with the task and to ensure that each subject understood task demands. It has been demonstrated that mentally retarded and nonretarded subjects must approach the experimental task with similar understandings of task demands in order for valid comparisons to be made (Maisto & Baumeister, 1984). All subjects demonstrated sufficient understanding of task demands within the span of the 10 practice trials by performing at or above an 80% accuracy criterion. Each subject was exposed to multiple exemplars of the nine possible Target × Distractor structural combinations in a single testing session. Subjects were exposed to a total of 132 experimental match-to-sample trials. The order of trials was randomized by the computer to ensure that subjects were not exposed to identical orders of trials. Each trial was preceded by the appearance of a visual cue on the computer monitor indicating the position of the impending target stimulus. Van Der Heijden, Wolters, Groep, and Hagenaar (1987) have demonstrated that foreknowledge of the position of the stimulus is beneficial in recognition experiments. The experimenter initiated each trial by pressing the space bar on the computer keyboard following a verbal indication of the subject's readiness to continue. When the space bar was pressed, the target stimulus appeared for either 50 ms or 100 ms, as discussed above. A backward visual mask of crosshatched lines then replaced the checkerboard pattern of the target stimulus. This backward visual masking procedure was necessary to eliminate any effects due to an afterimage appearing on the computer monitor, or an iconic afterimage (Kahneman, 1968). The masking figure remained on the screen until a response was made. Following an interstimulus interval of Is, a two-stimulus array appeared. The two-stimulus array consisted of a stimulus identical to the previously displayed target stimulus and a distractor stimulus. The target and distractor stimuli occupied the left and right positions in the array an equal number of times. The trial was completed when the subject responded by touching one of the two stimuli on the computer screen. A correct response was followed by a computer graphics display of a smiling face. If the subject's choice was incorrect, the screen remained blank for a 2-s interval prior to the initiation of the next trial.

DETECTION OF STIMULUSORGANIZATION

441

RESULTS Data for the match-to-sample trials were analyzed using 2(Group) by 3(Target Structure) by 3(Distractor Structure) analyses of variance (ANOVAs), with repeated-measures on the latter two factors. Significant effects from the analyses were followed by one-way ANOVAs and Newman-Keuls post hoc comparisons.

Recognition Data The lack of a main effect for Group revealed that the overall performance of the mentally retarded subjects did not differ significantly from that of the nonretarded subjects. However, the nonretarded subjects did perform slightly better than the mentally retarded subjects with mean percent correct recognitions for the groups being 79% (SD = .22) and 74% (SD = .25), respectively. The main effect for Target Structure, F(2, 56) = 2.69, p < . 10, MS e = 0.04, did approach significance due to a slight decline in performance with low structure targets. Mean percent correct recognitions in the high, moderate, and low structure target conditions were 78% (SD = .24), 78% (SD = . 18), and 74% (SD = .28), respectively. The main effect for Distractor Structure was significant, F(2, 56) = 5.57, p < .01, MSe = 0.03. More important, however, there was a significant Group x Distractor Structure interaction, F(2, 56) = 3.28, p < .05, MS~ = 0.03. These data indicated that the structure of the distractor did affect performance, and the effect differed for the two groups. The Group × Distractor Structure interaction is displayed in Figure 2. Post hoc analyses revealed, and it is evident from Figure 2, that the major difference between groups occurred with moderate structure Target l - - I Retarded O - - 0 Nonretarded

100

90

80

70

60

50 high

moderote

low

DISTRACTOR STRUCTURE

FIG. 2. Mean percent correct recognitions for the mentallyretarded and nonretarded subjects across levels of Distractor Structure.

442

SORACI, CARLIN, DECKNER. AND BAUMEISTER

distractors. In this condition, mentally retarded subjects performed much more poorly than nonretarded subjects. The Target Structure x Distractor Structure interaction, F(4, 112) = 2.61, p < .05, MS e = .05, also was significant. This interaction is depicted in Figure 3. This figure, therefore, depicts the overall means and standard errors for each of the nine conditions in the study. Post hoc analyses revealed a significant one-way interaction in the low structure distractor condition, F(2, 59) = 3.85, p < .05, MSe = .07. In this condition, the mean for the high structure target was significantly greater than the mean for the low structure target. This finding supported the hypothesis that stimuli dissimilar in organization would be easier to discriminate. Finally, the Group × Target Structure x Distractor Structure three-way interaction was not significant. The similarity of the Target Structure × Distractor Structure interactions for the mentally retarded and nonretarded subjects is evident from an inspection of Figure 4. It can be seen that the pattern of results is nearly identical for both groups despite the poorer performance of mentally retarded subjects with moderate structure distractors.

Stimulus Selection Detection Rates. Due to the potential for stimulus-specific response biases, overall detection rates for each stimulus in each of the structural categories were calculated. Overall detection rates for mentally retarded and nonretarded subjects for the three stimuli in each Target Structure and Distractor Structure condition are displayed in Table 2 (p. 444) and Table 3 (p. 444), respectively. These data indicated that stimulus-specific response biases were not a factor in the significant group effects obtained in the study. Target mHigh [ ~ Moderate I-7-1 Low

100

90

80

70

60

50

ii I11 high

moderate

low

DISTRACTOR STRUCTURE

FIG. 3. Overall mean percent correct recognitions and standard errors (SE) for each of the nine Target by Distractor Structure combinations.

DETECTION OF STIMULUS ORGANIZATION

443

Nonretarded Target IHigh I--'1 Moderate l--/q Low

100

90 "5 &) o (D

80

0)

o

13-

70

o: oJ 60

50 high

moderote

low

DISTRACTOR STRUCTURE

Mentally R e t a r d e d

Target I High U::3 Moderate EZ3 Low

100

90

t,D

80

70

60

50

high

moderate

low

DISTRACTOR STRUCTURE FIG. 4. Depiction of the Target by Distractor Structure interactions for the mentally retarded and nonretarded subjects.

Sorting Data. Ten graduate students at Vanderbilt University, unfamiliar with the study or the stimuli, were recruited to participate in a sorting task. Each subject was presented with the 12 stimuli from Figure 1, and instructed to sort the stimuli into four groups of any size (cf. Garner, 1974). The purpose of this study was to delineate the correspondence between the way in which the present authors have operationalized stimulus structure, and the way in which subjects actually discriminate particular stimuli. The overall percentage of stimuli grouped in accordance with the stimulus

444

SORACI, CARLIN, DECKNER, AND BAUMEISTER TABLE 2 Overall Detection Rates for Mentally Retarded and Nonretarded Subjects for the Three Stimuli in Each Target Structure Condition a Group Target Structure

High (HH) Moderate I (HL) Moderate 2 (LH) Low (LL)

Mentally Retarded

73, 72, 75, 70,

75, 73, 79, 64,

72 81 78 71

Nonretarded

78, 93, 76, 78,

77, 78, 73, 74,

90 87 79 85

Note. Values represent mean percent correct groupings for each individual stimulus across all distractor conditions. aThe moderate structure condition was divided into two groups for this analysis to represent the two types of mixed structure.

structure parameters c h o s e n in the study are presented in Figure 5. T h e s e data indicated that subjects e f f e c t i v e l y c a t e g o r i z e d the stimuli based upon the a priori structural categories c h o s e n for the c h e c k e r b o a r d stimuli in the detection task.

DISCUSSION In a recent study e x a m i n i n g e n c o d i n g processes in m e n t a l l y retarded and nonretarded individuals, Caruso and D e t t e r m a n (1983) found group differences only with respect to speed and error rates. Individuals in both groups r e s p o n d e d to the structural m a n i p u l a t i o n s in a similar manner. This led Caruso and D e t t e r m a n to c o n c l u d e that the typical differential p e r f o r m a n c e s on c o g n i t i v e tasks in groups differing in intelligence ( D e t t e r m a n , 1979) w e r e due to " v a r i a b l e s other than

TABLE 3 Overall Detection Rates for Mentally Retarded and Nonretarded Subjects for the Three Stimuli in Each Distractor Structure Condition a Group Distractor Structure

High (HH) Moderate 1 (HL) Moderate 2 (LH) Low (LL)

Mentally Retarded

82, 70, 69, 70,

74, 67, 73, 64,

82 81 69 71

Nonretarded

88, 80, 89, 78,

66, 78, 79, 74,

86 92 80 85

Note. Values represent mean percent correct groupings for each individual stimulus across all target conditions. ~The moderate structure condition was divided into two groups for this analysis to represent the two types of mixed structure.

DETECTION OF STIMULUSORGANIZATION

445

100 i 8o u I C.)

60, 1

co v 40 n

0

High (HH)

5

Moderete (HL,LH)

Low (LL)

Stimulus Structure

FIG. 5. Overall percentage of stimuli on the sorting task grouped in accordance with the stimulus structure parameters used in the study. those of stimulus structure" (p. 655). Given the results of the present study, Caruso and Detterman's conclusion may have been premature. The results of the present study indicated that mentally retarded and nonretarded individuals effectively and equivalently detected target stimuli when there was either (a) high structural organization of target and/or distractor stimuli, or (b) high target-distractor disparity. Detection rates of mentally retarded individuals, however, were substantially lower than those of controls with moderate levels of distractor organization. This condition can be characterized as one of reduced stimulus information, since it contains neither two highly encodable stimuli (i.e., high organization target and high organization distractor) nor salient interstimulus disparity (i.e., high organization target and low organization distractor or vice versa). Whereas both groups effectively utilized disparity in the high and low distractor conditions, nonretarded subjects had high detection rates at even moderate levels of distractor organization. These rates were equivalent to their performance at high levels of distractor organization. Since the moderate level of distractor organization contains minimal interstimulus disparity, the high detection rates observed in this condition suggested that the stimuli at the moderate level were more effectively encoded by nonretarded individuals than by mentally retarded individuals. Post hoc item analyses indicated that there were no differential detection rates a c r o s s stimuli within a given class. These results attested to the intraclass comparability of the stimuli used. It also should be noted in this context that the sorting task performance was consistent with detection performance. The fact

446

SORACI, CARLIN, DECKNER, AND BAUMEISTER

that subjects categorized the stimuli into groups which paralleled the structural organization categories used on the detection task suggests that the stimulus attributes comprising the checkerboard patterns in the present study were directly related to the discriminability of the stimuli. This pattern is also consistent with Uttal's (1983) position that detection and discrimination are related processes. Furthermore, the between- and within-groups variability typically encountered in comparisons of groups differing in intelligence (Baumeister, 1984) was not found in the present study. These observations indicated the potential utility of the present detection task in asessing rates of processing in groups differing in intelligence. The present findings are analogous to those the present investigators obtained with relational tasks such as oddity and auditory dishabituation (Soraci et al., 1986; Soraci, Baumeister, & Carlin, in press). Although these investigations utilized more global stimulus array organizations, differential performances between mentally retarded and nonretarded individuals were found only at the intermediate level of a particular stimulus structure or context. The similarity of the present results, obtained with manipulations of stimulus-specific organization, to those of our previous studies suggests a general hypothesis. Because most laboratory and naturally occurring stimuli are composed of moderate or mixed, rather than extreme, levels of organization, certain performance differences between mentally retarded and nonretarded individuals on cognitive processing tasks could be related to differential detection of moderate levels of stimulus organization. One important question for future research is the identification of other contexts in which the indicated differential performance occurs. Such identification could lead to the development of interventions that systematically take into account the influence of the organizational parameters of stimulus formats. In addition, since in the present study moderate organization was comprised of high levels of symmetry or adjacency (but not both), the relative contributions of symmetry and adjacency to detection performance is an important question left unresolved by the present results.

REFERENCES Alexander, C., & Carey, S. (1968). Subsymmetries.Perception & Psychophysics, 4, 73-77. Baumeister, A.A. (1984). Some methodological and conceptual issues in the study of cognitive processes with retarded people. In P.H. Brooks, R. Sperber, & C. McCauley(Eds.), Learning and cognition in the mentally retarded. Hillsdale, NJ: Erlbaum. Bornstein, M.H., & Stiles-Davis, J. (1984). Discrimination and memory for symmetry in young children. Developmental Psychology, 20, 637-649. Caruso, D.R. (1985). Influence of item identification on the memory performance of mentally retarded and nonretarded adults. Intelligence, 9, 51-68. Caruso, D.R., & Detterman, D.K. (1983). Stimulus encoding by mentallyretarded and nonretarded adults. American Journal of Mental Deficiency, 87, 649-655.

DETECTION OF STIMULUS ORGANIZATION

447

Chipman, S.F., & Mendelson, M.J. (1979). Influence of six types of visual structure on complexity judgments in children and adults. Journal of Experimental Psychology: Human Perception and Performance, 5, 365-378. Detterman, D.K. (1979). Memory in the mentally retarded. In N.R. Ellis (Ed.), Handbook of mental deficiency: Psychological theory and research (2nd ed.). Hillsdale, NJ: Erlbaum. Dinsmoor, J.A. (1985). The role of observing and attention in establishing stimulus control. Journal of the Experimental Analysis of Behavior, 43, 365-381. Garner, W.R. (1974). The processing of information and structure. Hillsdale, NJ: Erlbaum. Gibson, J.J. (1979). An ecological approach to visual perception. Boston: Houghton Mitilin. Howe, E.S. (1980). Effects of partial symmetry, exposure of time, and backward masking on judged goodness and reproduction of visual patterns. Quarterly Journal of Experimental Psychology, 32, 27-55. Kahneman, D. (1968). Method, findings, and theory in studies of visual masking. In R.N. Haber (Ed.), Information-processing approaches to visual perception. New York: Hart, Rinehart & Winston. Maisto, A.A., & Baumeister, A.A. (1984). Dissection of component process in rapid information processing tasks: Comparison of retarded and nonretarded people. In R. Sperber, C. McCauley, & P. Brooks (Eds.), Learning and cognition in the mentally retarded. Hillsdale, NJ: Erlbaum. Nettlebeck, T., & Lally, M. (1979). Age, intelligence, and inspection time. American Journal of Mental Deficiency, 83, 398-401. Palmer, S.E., & Hemenway, K. (1978). Orientation and symmetry: Effects of multiple, rotational, and near symmetries. Journal of Experimental Psychology: Human Perception and Performance, 4, 691-702. Sekuler, R., & Blake, R. (1985). Perception. New York: Alfred A. Knopf. Soraci, S.A., Jr., Barlean, J.L., Haenlein, M., & Baumeister, A.A. (1986). Lower sensitivity to alterations of auditory relational information in mentally retarded than in nonretarded adults. Physiological Psychology, 14, 146-149. Soraci, S.A., Jr., Baumeister, A.A., & Carlin, M,T. (in press). Stimulus organization and stimulus detection: Intelligence-related differences. In D.K. Detterman (Ed.), Current topics in human intelligence (Vol. 3). Norwood, NJ: Ablex. Soraci, S.A., Jr., Deckner, C.W., Haenlein, M., Baumeister, A.A., Murata-Soraci, K., & Blanton, R.L. (1987). Oddity performance in preschool children at risk for mental retardation: Transfer and maintenance. Research in Developmental Disabilities, 8, 137-151. Sperling, G. (1960). The information available in brief visual presentations. Psychological Monographs, 74, 1-29. Uttal, W.R. (1983). Visual form detection in 3-dimensional space, Hillsdale, NJ: Erlbaum. Van Der Heijden, A.H.C., Wolters, G., Groep, J.E., & Hagenaar, R. (1987). Single-letter recognition accuracy benefits from advance cuing of location. Perception & Psychophysics, 42,503509.