DeWeerd, P., Peralta, M. R., Desimone, R., & Ungerleider, L. G. (1999)
Nature neuroscience, 2(8), 753-758.
Many objects in natural visual scenes compete for attention. To identify the neural mechanisms necessary for visual attention, we made restricted lesions, affecting different quadrants of the visual field but leaving one quadrant intact, in extrastriate cortical areas V4 and TEO of two monkeys. Monkeys were trained to discriminate the orientation of a target grating surrounded by distracters. As distracter contrast increased, performance deteriorated in quadrants affected by V4 and TEO lesions, but not in the normal quadrant. Performance in affected quadrants was restored by increasing the contrast of the target relative to distracters. Thus, without V4 and TEO, visual attention is ‘captured’ by strong stimuli, regardless of their behavioral relevance.
Contribution to the field
This is the first paper showing that after lesions in extrastriate areas where neuronal selective attention mechanisms have been described, Macaque monkeys show a behavioral attention deficit. Specifically, the monkeys were unable to accurately perceive a target stimulus when it was surrounded by irrelevant distracters. Using our paradigm, others have demonstrated the same deficits after a V4 lesion in a human patient (Gallant et al., Neuron, 2000). Together, these data are relevant as they further strengthen the idea that similar selective attention mechanisms exist in Macaques and humans. We also found that in lesion-affected parts of the visual field, the relative contrast between the target and the surrounding distracters determined target discrimination capability, so that increasingly higher target contrasts (relative to distracters) rescued discrimination performance. Knowing that contrast is a stimulus feature that is strongly related to gamma frequency (Roberts et al., Neuron, 2013, see below), this finding is in line with a role of gamma frequency in regulating access to higher hierarchical levels in the case of competition among stimuli (Lowet et al., eLife, 2017, see below).