Abstract
Purpose :
We need to perceive the size of objects accurately to interact with the real world. However, the perceived size of an object could be biased by its surroundings. For example, in the Ebbinghaus illusion, the perceived size of a central target depends on the size of the surrounding inducers. The strength of this illusion correlates with the cortical magnification in human primary visual cortex (V1). Amblyopia, a neurodevelopmental disorder, is associated with abnormal cortical structure. In the current study, we measured the magnitude of Ebbinghaus illusion in control and amblyopic populations to investigate (1) whether the patients with amblyopia have normal object size perception, and (2) how their perception is affected by abnormal interocular interactions.
Methods :
Sixteen adult amblyopes and 16 controls participated in the experiment. There were two inducer sizes of the Ebbinghaus stimuli: small and large (Fig.1A). We measured the Ebbinghaus magnitude under binocular Bi, monocular MF and MA, and dichoptic DTF, DTA, DTPF, and DTPA viewing conditions (Fig.1B) using a pedestal task. The point of subjective equality (PSE) of the psychophysical function of the perceived size relative to the pedestal defined the magnitude of the illusion.
Results :
First, we compared the difference of the Ebbinghaus magnitude between the amblyopic and control group across the 7 viewing conditions. In the small inducers condition, we found a significant main effect of group (F1,30=5.42, P=0.027). The post hoc analysis showed that amblyopes had larger illusion magnitudes in MA (P<0.001) and DTA (P=0.016) conditions when compared to controls. For large inducers, the effect of group (F1,30=7.08, P=0.012) was also significant. But the illusion magnitude was significantly smaller for amblyopes in the MA, DTPF and DTPA conditions (P≤0.046). Within groups, we found that both the amblyopic and control group showed a decreased illusion magnitude in the dichoptic DTPF and DTPA conditions compared to the monocular viewing (P≤0.009).
Conclusions :
Our results showed that the patients with amblyopia exhibited a larger Ebbinghaus illusion magnitude with small inducers, but a smaller magnitude with large inducers, with either the amblyopic eye or dichoptic viewings. This impaired perception may be due to the abnormal cortical structure and function in the amblyopic brain, especially in V1.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.