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PURPOSE: The goal of the present study was to elucidate the neural mechanisms underlying processing global and local features in a non-human primate model.
METHODS: Monkeys were trained to make a saccade to an odd-ball target, which was different from the distractors (white circle) in color (red circle), local features (square), a global feature (ring) or their combinations. Saccade latencies were used to assess monkeys’ sensitivity to distinctions in color, local features and the global feature.
RESULTS: In the first experiment, the odd-ball target was presented simultaneously with the distractors. Contrary to predictions based on the general model, we found that detecting the global feature took less time than detecting the local features, but took about the same time as detecting color. In the second experiment, the distractors were presented first and one of them was replaced by the odd-ball target. Thus, monkeys were asked to detect a change in color, local features or a global feature in absence of target onset. Again, contrary to predictions of the general model, we found that detecting a change in the global feature (i.e., no hole vs. one hole) is faster than detecting a change in either color or local features. In the third experiment, we examined how distinctions in local and global features affect detecting distinction in color. We found that detecting distinction in color was facilitated by distinction in the global feature, but not in the local features. In the fourth experiment, we further examined interactions between detecting distinctions in local and global features. We found that distinction in local features of the ring-outside shape may facilitate detecting the ring, but distinction in local features of the ring-inside shape may slow detecting the ring.
CONCLUSIONS: These results not only challenge the general model of visual information processing by demonstrating monkeys’ sensitivity to a global feature over local features, but also provide insights into a new model, which features differential processing of local and global properties.