Effects of complex background scene on object selectivity of current source density activities in the macaque inferior temporal cortex

In our daily life, visual objects do not appear in isolation, but are embedded in a complex background. Furthermore, since objects are typically brought into the fovea by eye movements, there is a sudden change of the background just before the objects are foveated. Here we studied whether and how complex background and its sudden change affect the object-selective neuronal activities in the inferior temporal cortex of macaque monkeys by analyzing the current source density (CSD) signals, which reflect the local synaptic processes. We presented visual objects to analgesized and immobilized monkeys either (A) on a gray background, (B) on complex backgrounds during prolonged presentations of these backgrounds, or (C) on complex backgrounds that were switched from a gray background simultaneously with the appearance of the object. We found that the object preference of the object-selective CSD activity was considerably modified when objects were embedded in complex (condition B) instead of gray backgrounds (condition A), but the sudden change of background (condition C) canceled this modification and also enhanced the CSD response magnitude. We discuss the implications of these results to the visual processing in natural conditions such as active visual search of objects embedded in natural scenes