Spatio–Temporal Frequency Characteristics of Perceptual Filling–in

Abstract

Abstract: : Purpose: Perceptual filling–in is a famous illusion such that a small area (target), which is presented in peripheral vision and is surrounded by dynamic texture, appears as filled–in by the surrounding texture. Consequently, it becomes invisible within a few seconds. Time to filling–in depends on target and texture attributes, such as their spatial density, color or motion (Weerd et al. 1998, Welchman & Harris 2001). Because filling–in is considered as a phenomenon of the primary visual cortex (Weerd et al. 1995) and cells in the primary visual cortex have relatively simple spatio–temporal (S–T) frequency characteristics, investigation of filling–in from the viewpoint of S–T frequency characteristics of the target and the texture seems to be useful to understand the filling–in mechanism. This study is intended to measure S–T frequency characteristics of filling–in. Methods: Time to filling–in was measured under the condition that a homogeneous gray target is presented in peripheral human vision and is surrounded by dynamic textures which have various types of S–T spectrum. Luminance of the gray target is equal to the average luminance of the dynamic texture. Moreover, spatio–temporal frequency sensitivity in human peripheral vision was examined. Results: We first considered the following mathematical model on filling–in occurrence process. The model introduces a measure, called perceptual power (PP), representing the degree of distinguishability of the target from the surrounding texture. Initial PP is supposed to be represented as the inner product between the power spectrum of dynamic texture and S–T frequency sensitivity in human vision. PP decreases exponentially from an initial value while the surrounding dynamic texture is presented. Thereupon, filling–in appears when PP falls below a certain threshold value. We estimated model parameters using the experimental results: the initial value, threshold value and attenuation factor in PP decrement. The attenuation factor was proportional to the visual S–T frequency sensitivity in human vision with a correlation coefficient of 0.64. Conclusions: We concluded that the degree of distinguishability of the target from the surrounding texture affects the attenuation factor in PP decrement, not the time to filling–in itself. The attenuation factor is inferred to correlate with S–T frequency sensitivity. Attenuation of PP is caused by fatigue of the neural cells to which strong and successive stimuli are given.

Keywords: temporal vision • texture • perception