Lotfi B. Merabet¹ (), Claire E. Manley^1,2, Peter J. Bex²; ¹Massachusetts Eye & Ear, Harvard Medical School, ²Department Psychology, Northeastern University

The semantic relationships among real objects have been quantified in the THINGS image database. We used this database to investigate visual semantic behavior in individuals with cerebral (cortical) visual impairment (CVI), a brain-based visual disorder associated with higher-order visual processing deficits, including object recognition. Participants (8 CVI, mean age=20.13 years ±5.96 SD; 9 control, mean age=24.89 years ±11.57 SD) viewed a series of image pairs: one baseline pair and one experimental pair per trial, and determined which pair was more similar. In the baseline pair, one image was selected at random, and the second image differed by a pedestal of 0.1, 0.2, or 0.3 in semantic units. In the experimental pair, one image was selected at random, and the second image differed by an amount controlled by a 3-up-1-down staircase. Threshold semantic difference was estimated from the 75% point of a psychometric function fit to the proportion of ‘more different’ responses as a function of semantic distance across 60 trials. There was a significant pedestal effect [F(1,48)=38.82, p=1.204e-0] and group effect [F(1,49)=7.30, p=0.0095] on discrimination thresholds level, with semantic difference thresholds increasing as pedestal difference increased and thresholds being higher for the CVI group (0.1: 0.35±0.27 SD, 0.2: 0.54±0.24 SD, 0.3: 0.65±0.15 SD) than the control group (0.1: 0.12±0.08 SD, 0.2: 0.42±0.07 SD, 0.3: 0.50±0.05 SD). There was no evidence of internal noise effects. These findings suggest that individuals with CVI have greater difficulty distinguishing images of common objects, indicating a potential deficit in mental representations to interpret their visual environment.

Acknowledgements: NIH/NEI R01 EY030973