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Visual selective attention was investigated in children aged 5, 7 and 9 and in adults. The groups were compared on a filtering task in which conditions varied with regard to number (0, 2, 8) and location (close, far) of the non-relevant stimuli surrounding the targeted stimuli and the presence or absence of a solid-line border around the target stimuli. The results were analyzed with regard to development differences between the age groups. Contrary to expectations, the presence of non-relevant stimuli was not related to impaired performance nor was the presence of a solid-line border related to enhanced performance. No effect of border was found in any of the groups. However, the reaction times of older children and adults were faster with 8 non-relevant stimuli far from the target. Five year old children did not show this effect. This indicates that older children and adults can utilize this group of non-relevant stimuli as a tool to focus the attentional lens.

Six experiments tested the assumption that, in visual perception, observers have reliable and direct access to the equivalence of shapes in projective geometry (I call this "the invariance hypothesis in the theory of shape constancy"). This assumption has been made in the study of vision since Helmholtz's time. Two experiments tested recognition of the projective equivalence of planar shapes. In another four experiments, subjects estimated the apparent shape of a solid object from different perspectives. Departure from projective equivalence was assessed in each study by measuring the cross ratio for the plane. This measure of projective invariance is new to perceptual research. Projective equivalence was not found to be perceived uniformly in any of the studies. A significant effect of change in perspective was found in each study. These results were construed as supporting the classical theory of depth cues against the invariance hypothesis.

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A series of six studies investigated whether an amodal or modality-specific model of perception best accounted for auditory and visual processing of temporal patterns. Intramodal and intermodal pattern pairs were presented to subjects in a same-different paradigm. The first two studies found that performance on all modality pairs changed in parallel with age and complexity or delay. These data were consistent with the amodal model of perceptual processing: the modality of the patterns did not affect performance. The last four studies found that when considerably more difficult comparisons were combined with blocking on intramodal and intermodal trials a difference emerged between the two types of trials. Intramodal performance was superior to intermodal performance. The effect was subtle though and difficult to isolate. At no point in these studies was there evidence of modality-adeptness; visual and auditory processing of the temporal patterns was equally proficient. A multicoding model was proposed to accommodate these results, in general accord with information processing and amodal models of perception.

Persons with autism spectrum disorders (ASD) appear to be slower to interpret the meaning of symbolic cues. This could be because they are slower to read the symbolic cue, or because they are slower to select a response to the symbolic cue. Groups of participants with autism (n=11), participants with Asperger syndrome (n=9), and typically developing children (n=16) completed four forced-choice reaction time tasks to examine whether persons with ASD are slower to process the symbolic cue or slower to prepare a response to the cue. The participants completed two control conditions and two orienting conditions using non-predictive central arrow cues. In the Target and Cue conditions, participants gave a speeded response to the appearance of either a target (x) or a central arrow. In the Variable Cue Exposure (VCE) condition, the exposure time to the cue varied (100, 300, 600, or 1000 ms) and was followed by a 100 ms blank screen before the presentation of the target. In the Constant Cue Exposure (CCE) condition, all cues were presented for 100 ms and were followed by blank screens that varied in presentation length (100, 300, 600, or 1000 ms) before the presentation of the target. The results indicated that each group showed a unique pattern of responding. In both the Target and Cue conditions, participants with autism were slower than both Asperger syndrome and typically developing children. In both the VCE and CCE conditions, behavioural effects of the cue were found for participants with autism at longer SOAs than for Asperger syndrome, and at longer SOAs for Asperger syndrome than for typically developing children. These findings support the notion that persons with ASDs are impaired in their preparation of responses as opposed to impaired in reading the meaning of the cue. Further, both the ASD groups showed stronger facilitation effects at longer SOAs than typically developing children, indicating that they were less able to use cue predictability to mediate responding. The differences found between autism and Asperger syndrome are discussed in terms of developmental and clinical distinctions between the groups, and implications for theory and research design.

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