Effects of attention and distractor contrast on the responses of middle temporal area neurons to transient motion direction changes.

The ability of primates to detect transient changes in a visual scene can be influenced by the allocation of attention, as well as by the presence of distractors. We investigated the neural substrates of these effects by recording the responses of neurons in the middle temporal area (MT) of two monkeys while they detected a transient motion direction change in a moving target. We found that positioning a distractor near the target impaired the change-detection performance of the animals.

Multifocal attention filters targets from distracters within and beyond primate MT neurons' receptive field boundaries.

Visual attention has been classically described as a spotlight that enhances the processing of a behaviorally relevant object. However, in many situations, humans and animals must simultaneously attend to several relevant objects separated by distracters. To account for this ability, various models of attention have been proposed including splitting of the attentional spotlight into multiple foci, zooming of the spotlight over a region of space, and switching of the spotlight among objects.

Expansion of MT neurons excitatory receptive fields during covert attentive tracking.

Primates can attentively track moving objects while keeping gaze stationary. The neural mechanisms underlying this ability are poorly understood. We investigated this issue by recording responses of neurons in area MT of two rhesus monkeys while they performed two different tasks.

Neuronal activity in the visual cortex reveals the temporal order of cognitive operations.

Most mental processes consist of a number of processing steps that are executed sequentially. The timing of the individual mental operations can usually only be estimated indirectly, from the pattern of reaction times. In vision, however, many processing steps are associated with the modulation of neuronal activity in early visual areas.

A metric-based analysis of the contribution of spike timing to contrast and motion direction coding by single neurons in macaque area MT.

Spike timing is thought to contribute to the coding of motion direction information by neurons in macaque area MT. Here, we examined whether spike timing also contributes to the coding of stimulus contrast. We applied a metric-based approach to spike trains fired by MT neurons in response to stimuli that varied in contrast, or direction.

Frequency-dependent attentional modulation of local field potential signals in macaque area MT.

Visual attention modulates neuronal responses in primate motion processing area MT. However, whether it modulates the strength local field potentials (LFP-power) within this area remains unexplored, as well as how this modulation relates to the one of the neurons' response. We investigated these issues by simultaneously recording LFPs and neuronal responses evoked by moving random dot patterns of varying direction and contrast in area MT of two male monkeys (Macaca mulatta) during different behavioral conditions.

Attention differentially modulates similar neuronal responses evoked by varying contrast and direction stimuli in area MT.

The effects of attention on the responses of visual neurons have been described as a scaling or additive modulation independent of stimulus features and contrast, or as a contrast-dependent modulation. We explored these alternatives by recording neuronal responses in macaque area MT to moving stimuli that evoked similar firing rates but varied in contrast and direction. We presented two identical pairs of stimuli, one inside the neurons' receptive field and the other outside, in the opposite hemifield.

Different processing phases for features, figures, and selective attention in the primary visual cortex.

Our visual system imposes structure onto images that usually contain a diversity of surfaces, contours, and colors. Psychological theories propose that there are multiple steps in this process that occur in hierarchically organized regions of the cortex: early visual areas register basic features, higher areas bind them into objects, and yet higher areas select the objects that are relevant for behavior. Here we test these theories by recording from the primary visual cortex (area V1) of monkeys.

Attention lights up new object representations before the old ones fade away.

We investigated how attention shifts from one object to another by recording neuronal activity in the primary visual cortex. Monkeys performed a contour-grouping task in which they had to select a target curve and ignore a distractor curve. Some trials required a shift of attention, because the target and distractor curves were switched during the course of the trial.

Visual information transfer across eye movements in the monkey.

During normal viewing, the eyes move from one location to another in order to sample the visual environment. Information acquired before the eye movement facilitates post-saccadic processing. This "preview effect" indicates that some information is maintained in transsaccadic memory and combined with information acquired at the next fixation.

Correlates of transsaccadic integration in the primary visual cortex of the monkey.

We make several eye movements per second when we explore a visual scene. Each eye movement sweeps the scene's projection across the retina and changes its representation in retinotopic areas of the visual cortex, but we nevertheless perceive a stable world. Here we investigate the neuronal correlates of visual stability in the primary visual cortex.

Subtask sequencing in the primary visual cortex.

Complex visual tasks can usually be decomposed into a number of simpler subtasks. Whether such subtasks are solved serially or in parallel is subject to considerable debate. Here we investigate how subtasks are coordinated in time by recording from the primary visual cortex of macaque monkeys.