Distracter suppression dominates attentional modulation of responses to multiple stimuli inside the receptive fields of middle temporal neurons.

Single-cell studies in macaques have shown that attending to one of two stimuli, positioned inside a visual neuron's receptive field (RF), modulates the neuron's response to reflect the features of the attended stimulus. Such a modulation has been described as a 'push-pull' effect relative to a reference response: a neuron's response increases when attention is directed to a preferred stimulus, and decreases when attention is directed to a non-preferred stimulus. It has been further suggested that the response increase when attending to a preferred stimulus is the predominant effect. Here, we show that the observed attentional modulation depends on the reference response. We recorded neuronal responses in motion processing area middle temporal (MT) of macaques to two moving random dot patterns positioned inside neurons' RF. One pattern always moved in the neuron's antipreferred direction (null pattern), while the other moved in one of 12 directions (tuning pattern). At the beginning of a trial, a cue indicated the location and direction of the target. The animal was required to release a lever when a change in the target direction occurred, and to ignore changes in the distracter. Relative to neurons' initial responses to the dual stimuli (when attention was less likely to modulate responses), attending to the tuning pattern did not significantly modulate responses over time. However, attending to the null pattern progressively decreased responses over time. These results were quantitatively described by filter and input gain models, characterising a predominant response suppression relative to a reference response, rather than response enhancement.

Binocular rivalry of spiral and linear moving random dot patterns in human observers.

Binocular rivalry describes the alternating perception of two competing monocular images. It is hypothesized to arise at multiple levels of the visual pathway due to competition between neuronal populations representing the displayed images. We tested whether an enhanced neural representation of expanding motion yields a bias over other spiral motion (i.e., contraction and rotation) and linear motion stimuli during binocular rivalry. We presented random dot patterns of different motion types (i.e., linear and spiral), matched in contrast and speed, to human subjects through a mirror stereoscope. During spiral rivalry, expansion rivalry periods dominated over those of contraction and rotation, and contraction dominated over rotation. During linear motion rivalry, up, down, left, and right directions had similar rivalry periods. All spiral motions dominated over linear motions. Interestingly, when these motion types rivaled against each other, the rivalry periods of spiral motion slightly decreased while those of linear motion significantly increased. This rivalry also caused the bias for expansion relative to other spirals to disappear. Our results suggest a correlation between neuronal representations of different moving patterns and their perception during binocular motion rivalry and provide further evidence that rivalry periods are constrained by the ecologic relevance of stimuli.

Generalizing Duchenne to sad expressions with binocular rivalry and perception ratings.

Discrete emotion theories emphasize the modularity of facial expressions, while functionalist theories suggest that a single facial action may have a common meaning across expressions. Smiles involving the Duchenne marker, eye constriction causing crow's feet, are perceived as intensely positive and sincere. To test whether the Duchenne marker is a general index of intensity and sincerity, we contrasted positive and negative expressions with and without the Duchenne marker in a binocular rivalry paradigm. Both smiles and sad expressions involving the Duchenne marker were perceived longer than non-Duchenne expressions, and participants rated all Duchenne expressions as more affectively intense and more sincere than their non-Duchenne counterparts. Correlations between perceptual dominance and ratings suggested that the Duchenne marker increased the dominance of smiles and sad expressions by increasing their perceived affective intensity. The results provide evidence in favor of Darwin's hypothesis that specific facial actions have a general function (conveying affect intensification and sincerity) across expressions. (PsycINFO Database Record (c) 2019 APA, all rights reserved).