Abstract
To investigate how information is passed from the inferior temporal cortex (ITC) to other brain regions to enable stimuli to be selected from natural scenes for action, we analysed the responses of single and simultaneously recorded ITC neurons to stimuli presented in complex natural backgrounds. The macaques had to search for two objects on a screen, and a touch of one object was rewarded with juice, and of another object was punished with saline. The magnitudes of the responses of the neurons were similar when the (9×7deg) object was at the fovea in the real scene and with the plain background; but typically the receptive field sizes were much smaller in the real scene (36 deg) than in the plain background (65 deg). Simply introducing a second 10 deg stimulus into the experiment produced some of the effect produced by a complex background (with the receptive field reduced from 65 to 42 deg). In addition to these effects produced purely by introducing a background or second stimulus, attention also influenced the responses. When two stimuli were present in the plain background, the receptive field size was larger (42 deg) when a stimulus was a target for action than when the stimulus was not a target for action (24 deg). Interestingly, the effects of object-based attention were less marked when a complex background was present. When smaller objects (4.5×3.5 deg) were used, the receptive fields became even smaller (e.g. extending less than 10 deg beyond the stimulus). Thus a reduction in receptive field size of inferior temporal cortex neurons is produced by a complex background, and this contributes to facilitating the read-out of information about objects from the inferior temporal cortex, with only a small additional role for object-based attention (see Rolls,ET and Deco,G, 2002, Computational Neuroscience of Vision, Oxford University Press).
Research supported by the Wellcome Trust and the MRC IRC for Cognitive Neuroscience.