An Extended Normalization Model of Attention Accounts for Feature-Based Attentional Enhancement of Both Response and Coherence Gain.

Philipp Schwedhelm,B. Suresh Krishna,Stefan Treue,Matthias Bethge

doi:10.1371/journal.pcbi.1005225

Abstract

Paying attention to a sensory feature improves its perception and impairs that of others. Recent work has shown that a Normalization Model of Attention (NMoA) can account for a wide range of physiological findings and the influence of different attentional manipulations on visual performance. A key prediction of the NMoA is that attention to a visual feature like an orientation or a motion direction will increase the response of neurons preferring the attended feature (response gain) rather than increase the sensory input strength of the attended stimulus (input gain). This effect of feature-based attention on neuronal responses should translate to similar patterns of improvement in behavioral performance, with psychometric functions showing response gain rather than input gain when attention is directed to the task-relevant feature. In contrast, we report here that when human subjects are cued to attend to one of two motion directions in a transparent motion display, attentional effects manifest as a combination of input and response gain. Further, the impact on input gain is greater when attention is directed towards a narrow range of motion directions than when it is directed towards a broad range. These results are captured by an extended NMoA, which either includes a stimulus-independent attentional contribution to normalization or utilizes direction-tuned normalization. The proposed extensions are consistent with the feature-similarity gain model of attention and the attentional modulation in extrastriate area MT, where neuronal responses are enhanced and suppressed by attention to preferred and non-preferred motion directions respectively.

Highlights

Attention to visual features like a specific orientation or motion direction has been shown to enhance visual responses to the attended feature across visual cortex in both monkey neurophysiology [1] and human fMRI data [2,3,4]
We report a pattern of feature-based attentional effects on human psychophysical performance, which cannot be accounted for by the Normalization Model of Attention using biologically plausible parameters
The Normalization Model of Attention (NMoA) predicts that, assuming biologically plausible parameters [19], attention to a visual feature will impact neuronal responses mainly by increasing the effective response of neurons tuned to the attended feature, rather than by increasing the sensory input strength of the attended stimulus

Summary

Introduction

Attention to visual features like a specific orientation or motion direction has been shown to enhance visual responses to the attended feature across visual cortex in both monkey neurophysiology [1] and human fMRI data [2,3,4]. The NMoA predicts that, assuming biologically plausible parameters (see Materials and Methods) [19], attention to a visual feature will impact neuronal responses mainly by increasing the effective response of neurons tuned to the attended feature (response gain), rather than by increasing the sensory input strength of the attended stimulus (input gain). This implies, given a quasi-linear linking-model relating neuronal responses to behavioral output [20], that attention to a visual feature will not produce input-gain effects, but only response-gain effects on psychometric functions. Herrmann et al [19] confirmed this prediction when they observed only response gain effects in an experiment where human subjects paid attention to either narrow or broad ranges of orientation

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