Time to investigate human visual shape perception and recognition

点击翻译按钮获取中文摘要

The research proposed aims to determine the nature and time course of the visual information subtending the early routing of processing toward category-specialized mechanisms for visual object recognition (VOR) in humans and the operation of category-specialized mechanisms for the visual recognition of items in terms of their unique identity. We also aim to investigate the functional impact of growing receptive field sizes as processing moves up the hierarchy of visual areas in the human cortex. These studies will help resolve outstanding issues pertaining to our understanding of some of the most fundamental features of the human VOR system. To determine processing time course, we will be using a new psychophysical technique we have developed, which is random temporal sampling [see ref. 2]. This method can reveal how processing effectiveness evolves through time as well as temporal features of processing which are extremely replicable across individuals and also highly discriminant of the stimulus class and/or task participants perform. Regarding the visual information subtending VOR, two approaches will be used. One is the analysis of the spatial features of a large collection of images from different categories (faces, places, objects, and words) using discrete wavelet decomposition (DWT). The interest of DWT is that images are processed by a local operator (Daubechies wavelet) which provides localized information about the scale (i.e. spatial extent) and orientation of image contrasts. These functional features match those of the human primary visual cortex (V1). The DWT image descriptions will serve to characterize the visual contrasts between stimulus categories as well as the types of discrimination required for stimulus identification in these categories. The other method is the ideal observer model with either unlimited processing capacity or with an access to visual information restricted similarly to human low-level visual encoding (i.e. contrast-sensitivity function, oblique effect and reduction of visual acuity with increasing eccentricity). Divergences between the results of human participants and the ideal observers reveal processing limitations and/or biases intrinsic to the human visual system. The studies proposed will offer a rich, robust set of data on fundamental properties of VOR in humans. This outcome is expected to strongly stimulate future research and to contribute to the formulation of VOR theories with better explanatory power than those available today. COVID19 contingency plan: Due to COVID19, the three testing rooms in our lab have been reorganized such that we can maintain a minimum 2 meter distance from participants at all times. Both the equipment presently available and that requested in our concurrent NSERC Research tools and instruments application are fully compatible with this organization and we thus estimate future interruptions in the lab operations due to the pandemic as highly unlikely.