The properties of collinear facilitation in human vision /

The detection threshold of a luminance-defined Gabor is improved by two high contrast, aligned flanking Gabors, an effect termed collinear facilitation. However, the neural basis of collinear facilitation is not well understood. This thesis focuses on a number of issues in collinear facilitation to better our understanding of its neural basis. (1) Cortical sites: the cortical site of collinear facilitation was investigated, and results showed that collinear facilitation is a purely monocular phenomenon. (2) Temporal properties: Collinear facilitation has fast dynamics for initiation and once collinear facilitation occurs it either decays slowly or is associated with a sustained detection. (3) Selectivity to other types of stimuli: chromatic stimuli (which isolated the S-cone opponent and the L/M cone opponent mechanisms) and 2nd order stimuli (a 2D white noise or ID noise multiplied with a Gabor envelope) were used and the results showed that collinear facilitation occurs in chromatic processing, and that some 2nd order stimuli also exhibit collinear facilitation. However, there was no interaction between luminance and chromatic systems nor between 1st and 2nd order mechanisms, suggesting independent processing streams for collinear facilitation. All of these results supported the conclusion that collinear facilitation is not a general property of cortical neurons in V1 since most V1 neurons are binocular, sensitive to both chromatic and achromatic stimuli and sensitive to both 1 st and 2nd order stimuli. Furthermore, the temporal properties of collinear facilitation suggest complex dynamic interactions, not simply explained by the passive propagation of long-range recurrent intra-cortical connections between flanks and target