The hole precedence in face but not figure discrimination and its neuronal correlates

Rapid Processing of a Global Feature in the ON Visual Pathways of Behaving Monkeys

Visual objects are recognized by their features. Whereas, some features are based on simple components (i.e., local features, such as orientation of line segments), some features are based on the whole object (i.e., global features, such as an object having a hole in it). Over the past five decades, behavioral, physiological, anatomical, and computational studies have established a general model of vision, which starts from extracting local features in the lower visual pathways followed by a feature integration process that extracts global features in the higher visual pathways. This local-to-global model is successful in providing a unified account for a vast sets of perception experiments, but it fails to account for a set of experiments showing human visual systems' superior sensitivity to global features. Understanding the neural mechanisms underlying the "global-first" process will offer critical insights into new models of vision. The goal of the present study was to establish a non-human primate model of rapid processing of global features for elucidating the neural mechanisms underlying differential processing of global and local features. Monkeys were trained to make a saccade to a target in the black background, which was different from the distractors (white circle) in color (e.g., red circle target), local features (e.g., white square target), a global feature (e.g., white ring with a hole target) or their combinations (e.g., red square target). Contrary to the predictions of the prevailing local-to-global model, we found that (1) detecting a distinction or a change in the global feature was faster than detecting a distinction or a change in color or local features; (2) detecting a distinction in color was facilitated by a distinction in the global feature, but not in the local features; and (3) detecting the hole was interfered by the local features of the hole (e.g., white ring with a squared hole). These results suggest that monkey ON visual systems have a subsystem that is more sensitive to distinctions in the global feature than local features. They also provide the behavioral constraints for identifying the underlying neural substrates.

Shape predominant effect in pattern recognition of geometric figures of rhesus monkey

Three monkeys were trained successively with discrimination, concurrent matching to sample, and sameness-difference judgment tasks in which learning curves were compared. Then, the display duration for the stimuli was shortened to 100, 50, and 30 ms respectively to test the changes in accuracy and reaction time. All results in three experimental paradigms suggested consistently that the geometric shape (triangle, circle, and square) plays a more predominant role than topological features (the hole inside of a figure and the hole numbers) in monkey figure recognition. The results are different from the experiment by human subjects who presented hole predominant in figure recognition. Therefore, the precedence in perception depends on subject species, stimulus set, and ecological significance of the perceiving process.