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We examined how attention affected the orientation tuning of 262 isolated neurons in extrastriate area V4 and 135 neurons in area V1 of two rhesus monkeys. The animals were trained to perform a delayed match-to-sample task in which oriented stimuli were presented in the receptive field of the neuron being recorded. On some trials the animals were instructed(More)
Measurements of contrast sensitivity were obtained from isolated neurons in the lateral geniculate nucleus, striate cortex, and middle temporal visual area of macaque monkeys. Between the lateral geniculate nucleus and the middle temporal area contrast sensitivity functions become progressively steeper. Furthermore, many neurons in the middle temporal area(More)
The cortical and subcortical connections of the middle temporal visual area (MT) of the macaque monkey were investigated using combined injections of [3H]proline and horseradish peroxidase within MT. Cortical connections were assigned to specific visual areas on the basis of their relationship to the pattern of interhemispheric connections, revealed by(More)
Previous single-unit studies of visual cortex have reported that spatial attention modulates responses to different orientations and directions proportionally, such that it does not change the width of tuning functions for these properties. Other studies have suggested that spatial attention causes a leftward shift in contrast response functions, such that(More)
To determine the physiological mechanisms underlying the enhancement of performance by attention, we examined how attention affects the ability of isolated neurons to discriminate orientation by investigating the reliability of responses with and without attention. Recording from 262 neurons in cortical area V4 while two rhesus macaques did a delayed(More)
The visual system is constantly inundated with information received by the eyes, only a fraction of which seems to reach visual awareness. This selection process is one of the functions ascribed to visual attention. Although many studies have investigated the role of attention in shaping neuronal representations in the visual cortex, few have focused on(More)
Although most studies of visual attention have examined the effects of shifting attention between different locations in the visual field, attention can also be directed to particular visual features, such as a color, orientation or a direction of motion. Single-unit studies have shown that attention to a feature modulates neuronal signals in a range of(More)
Visual object recognition is computationally difficult because changes in an object's position, distance, pose, or setting may cause it to produce a different retinal image on each encounter. To robustly recognize objects, the primate brain must have mechanisms to compensate for these variations. Although these mechanisms are poorly understood, it is(More)
During cognitive tasks electrical activity in the brain shows changes in power in specific frequency ranges, such as the alpha (8-12 Hz) or gamma (30-80 Hz) bands, as well as in a broad range above ∼80 Hz, called the high-gamma band. The role or significance of this broadband high-gamma activity is unclear. One hypothesis states that high-gamma oscillations(More)