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Thursday, May 7, 2009
Northwest Hall (Chicago Hilton)
11:00 AM
Background: Visual processing of information by individuals with autism spectrum disorders (ASDs) is different to normally developing individuals. One aspect of the visual sense is the retinotopic representation of visual space within the visual cortex. How visual space is represented in the visual cortex is of interest because individuals with ASD display higher performance in visual search tasks. One factor that may affect performance on visual search tasks is crowding. In normal observers, identification of items in the visual periphery is impaired when other items are nearby. A reduced susceptibility to visual crowding may be the reason that individuals on the autism spectrum have been reported capable of outperforming normal observers in visual search for ellipses.
Objectives: To ascertain acuities for elliptical eccentricity and the critical spacings at which crowding impairs object identification.
Methods: Participants for this study were selected from a panel of volunteers that were matched for verbal, performance and full IQ. ASD participants met DSM-IV criteria confirmed by ADOS and review of clinical notes. Ethical approval was granted by University Ethics committee. Preliminary data have been collected from 6 ASD participants and 2 matched control subjects. We anticipate a total of 15 observers from each group.
An iMAC 7.1 computer running MATLAB™ (MathWorks Ltd) was used for stimulus generation, experiment control and recording subjects' responses. The programs controlling the experiment incorporated elements of the PsychToolbox. Stimuli were displayed on an ATI Radeon HD 2600 Pro monitor (1680 x 1050 pixels), driven by the computer's built-in graphics card. The observer was seated at 70 cm from the screen using their habitual optical correction if required. A central white spot 3 x 3 pixels was used for fixation. Short (120 ms) presentations guaranteed that our observers were unable to initiate an eye movement prior to the disappearance of our elliptical targets, which appeared at E = 3.9 deg, randomly to the left or the right of the fixation spot.
In the first phase of the experiment an adaptive staircase was used to converge on the 'threshold' elliptical eccentricity required for observers to discriminate between vertical and horizontal ellipses with 81% accuracy. In the second phase two circles flanked the target on its left and right. Each target's elliptical eccentricity was fixed at √2 times the observer's threshold. An adaptive staircase converged on the ‘critical' target-flanker distance with which the target's orientation could once again be identified with 81% accuracy.
Results: All results are expressed as mean ± sd. Acuity (1/threshold) was 3.50 ± 0.98 for the ASD group and 4.81 ± 1.38 for the matched participant group. The difference between groups was not significant (unpaired, two-tailed T-test: p=0.06). Critical spacing was 0.58E ± 0.11E for the ASD group and 0.62E ± 0.17E for the matched participants. Again, the difference was not significant (p=0.66).
Conclusions: These preliminary findings indicate that there are no differences in acuity or the effects of crowding between individuals with ASD and the comparison group.
Objectives: To ascertain acuities for elliptical eccentricity and the critical spacings at which crowding impairs object identification.
Methods: Participants for this study were selected from a panel of volunteers that were matched for verbal, performance and full IQ. ASD participants met DSM-IV criteria confirmed by ADOS and review of clinical notes. Ethical approval was granted by University Ethics committee. Preliminary data have been collected from 6 ASD participants and 2 matched control subjects. We anticipate a total of 15 observers from each group.
An iMAC 7.1 computer running MATLAB™ (MathWorks Ltd) was used for stimulus generation, experiment control and recording subjects' responses. The programs controlling the experiment incorporated elements of the PsychToolbox. Stimuli were displayed on an ATI Radeon HD 2600 Pro monitor (1680 x 1050 pixels), driven by the computer's built-in graphics card. The observer was seated at 70 cm from the screen using their habitual optical correction if required. A central white spot 3 x 3 pixels was used for fixation. Short (120 ms) presentations guaranteed that our observers were unable to initiate an eye movement prior to the disappearance of our elliptical targets, which appeared at E = 3.9 deg, randomly to the left or the right of the fixation spot.
In the first phase of the experiment an adaptive staircase was used to converge on the 'threshold' elliptical eccentricity required for observers to discriminate between vertical and horizontal ellipses with 81% accuracy. In the second phase two circles flanked the target on its left and right. Each target's elliptical eccentricity was fixed at √2 times the observer's threshold. An adaptive staircase converged on the ‘critical' target-flanker distance with which the target's orientation could once again be identified with 81% accuracy.
Results: All results are expressed as mean ± sd. Acuity (1/threshold) was 3.50 ± 0.98 for the ASD group and 4.81 ± 1.38 for the matched participant group. The difference between groups was not significant (unpaired, two-tailed T-test: p=0.06). Critical spacing was 0.58E ± 0.11E for the ASD group and 0.62E ± 0.17E for the matched participants. Again, the difference was not significant (p=0.66).
Conclusions: These preliminary findings indicate that there are no differences in acuity or the effects of crowding between individuals with ASD and the comparison group.