Attention and normalization circuits in macaque V1.
Bottom Line: Surround/mask stimuli provide an estimate to what extent V1 neurons are affected by normalization, which was compared against effects of spatial top down attention.In one class of models, attention contributed to normalization mechanisms, whereas in a different class of models it did not.Model selection based on Akaike's and on Bayesian information criteria demonstrated that in most cells the effects of attention were best described by models where attention did not contribute to normalization mechanisms.
Affiliation: Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.Show MeSH
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Mentions: The surround stimulus used was identical for all cells. The specific distribution of orientations present in the surround might therefore yield different effects on neurons, depending on their preferred orientation. This argument is based on the established differential effects of iso- and cross-orientation inhibition (Sengpiel et al., 1998; Jones et al., 2001, 2002; Freeman et al., 2002). Therefore we calculated the suppression index (SI) for each neuron and plotted this against the neuron's preferred orientation (Fig.3A). Neurons with stronger SI (larger than the median of the population) showed no obvious clustering around specific orientations, and there was also no obvious relationship between strength of SI, preferred orientation of a neuron and clustering of surround orientations (Fig.3B).
Affiliation: Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.