Integration of Local Features into Global Shapes

Abstract

The integration of local image features into global shapes was investigated in monkeys and humans using fMRI. An adaptation paradigm was used, in which stimulus selectivity was deduced by changes in the course of adaptation of a pattern of randomly oriented elements. Accordingly, we observed stronger activity when orientation changes in the adapting stimulus resulted in a collinear contour than a different random pattern. This selectivity to collinear contours was observed not only in higher visual areas that are implicated in shape processing, but also in early visual areas where selectivity depended on the receptive field size. These findings suggest that unified shape perception in both monkeys and humans involves multiple visual areas that may integrate local elements to global shapes at different spatial scales.

Distributed Neural Plasticity for Shape Learning in the Human Visual Cortex

“…In particular, the recognition of low-salience targets in cluttered scenes entails integration of features to global configurations and figure–ground segmentation. These processes are known to involve both early and higher visual areas [26]. The similar fMRI responses for low-salience shapes in the LOC and the early visual areas (F 5,50 < 1, p = 0.77) are consistent with the involvement of both early and higher visual areas in the detection of shapes in noise.…”

“…Thirty-two symmetrical and 32 asymmetrical shapes were rendered with collinear Gabor elements (0.55°) and embedded in backgrounds of randomly-positioned Gabors (0.55°), as described previously [26]. Each stimulus covered an area 14.35° × 14.35° (average shape area: 7.72° × 7.78°) and was presented 0.19° to the left or right of fixation.…”

“…Each run had 25 experimental trials for each condition (trained and untrained) and 25 fixation trials; that is, a total of 75 trials. A new trial began every 3 s and consisted of a stimulus image presented for 300 ms and a blank interval of 2,700 ms. As in previous studies [26], the order of presentation was counterbalanced so that trials from each condition, including the fixation condition, were preceded equally often by trials from each of the other conditions. In total, 100 trials were collected for each experimental condition across the four runs in each scanning session.…”

“…These aligned contours have been shown to result from the integration of the similarly oriented elements into global configurations [23–25]. Previous work has shown that these stimuli involve processing in both early retinotopic and higher occipitotemporal regions [26]. In Experiment 1, observers were presented with low-salience stimuli in which shapes were embedded in a background of randomly positioned and oriented Gabors.…”

The statistics of lines in natural images and implications for visual detection

“…Evidence supporting this comes from fMRI investigations in monkeys and humans: The neurons in V1 show higher response when viewing a long extended line, compared to randomly oriented segments of the line [11]. Here, we address the characteristics of the lateral connections from the perspective of information theory [12,13,14,15,16,17].…”