Biased competition through variations in amplitude of γ-oscillations

Experiments in visual cortex have shown that the firing rate of a neuron in response to the simultaneous presentation of a preferred and non-preferred stimulus within the receptive field is intermediate between that for the two stimuli alone (stimulus competition). Attention directed to one of the stimuli drives the response towards the response induced by the attended stimulus alone (selective attention). This study shows that a simple feedforward model with fixed synaptic conductance values can reproduce these two phenomena using synchronization in the gamma-frequency range to increase the effective synaptic gain for the responses to the attended stimulus. The performance of the model is robust to changes in the parameter values. The model predicts that the phase locking between presynaptic input and output spikes increases with attention

Object Detection in Natural Scenes By Feedback

Current models of object recognition generally assume a bottom-up process within a hierarchy of stages. As an alternative, we present a top-down modulation of the processed stimulus information to allow a goal-directed detection of objects within natural scenes. Our procedure has its origin in current findings of research in attention which suggest that feedback enhances cells in a feature-specific manner. We show that feedback allows discrimination of a target object by allocation of attentional resources

Attentional selection for object recognition - a gentle way

Abstract. Attentional selection of an object for recognition is often modeled using all-or-nothing switching of neuronal connection pathways from the attended region of the retinal input to the recognition units. However, there is little physiological evidence for such all-or-none modulation in early areas. We present a combined model for spatial attention and object recognition in which the recognition system monitors the entire visual field, but attentional modulation by as little as 20 % at a high level is sufficient to recognize multiple objects. To determine the size and shape of the region to be modulated, a rough segmentation is performed, based on pre-attentive features already computed to guide attention. Testing with synthetic and natural stimuli demonstrates that our new approach to attentional selection for recognition yields encouraging results in addition to being biologically plausible.

Vision out of the corner of the eye

The margin of the temporal visual field lies more than 90 degrees from the line of sight and is critical for detecting incoming threats and for balance and locomotive control. We show (i) contrast sensitivity beyond 70 degrees is higher for moving stimuli than for stationary, and in the outermost region, only moving stimuli are visible; (ii) sensitivity is highest for motion in directions near the vertical and horizontal axes and is higher for forward than for backward directions; (iii) the former anisotropy arises early in the visual pathway; (iv) thresholds for discriminating direction are lowest for upward and downward motion