How does the saccadic movement system select a target when visual, auditory, and planned movement commands differ? How do retinal, head-centered, and motor error coordinates interact during the selection process? Recent data on superior colliculus (SC) reveal a spreading wave of activation across buildup cells the peak activity of which covaries with the current gaze error. In contrast, the locus of peak activity remains constant at burst cells, whereas their activity level decays with residual gaze error. A neural model answers these questions and simulates burst and buildup responses in visual, overlap, memory, and gap tasks. The model also simulates data on multimodal enhancement and suppression of activity in the deeper SC layers and suggests a functional role for NMDA receptors in this region. In particular, the model suggests how auditory and planned saccadic target positions become aligned and compete

this paper we have used functional MRI (fMRI) to identify the neural systems implicated in attending to visual motion

Neurons in the middle temporal visual area (MT) of macaque cerebral cortex are highly selective for the direction of mo-tion but not the color of a moving stimulus. Recent experi-ments have shown, however, that the directional selectivity of many MT neurons persists even when a moving stimulus is defined solely by chromatic variation (Charles and Lo-gothetis, 1989; Saito et al., 1989; Dobkins and Albright, 1991a,b; Movshon et al., 1991; Gegenfurtner et al., 1994). To illuminate the mechanisms by which area MT uses color as a cue for motion correspondence, we recorded from MT neurons while rhesus monkeys viewed an “apparent mo-tion ” stimulus in which red/green sine wave gratings un-derwent contrast reversal each time they were displaced in a particular direction. Under such conditions, correspon-dence based upon chromatically defined borders conflicts

We investigated how the brain selects the targets for eye movements, a process in which the outcome of visual pro-cessing is converted into guided action. Macaque monkeys were trained to make a saccade to fixate a salient target presented either alone or with multiple distracters during visual search. Neural activity was recorded in the frontal eye field, a cortical area at the interface of visual process-ing and eye movement production. Neurons discharging after stimulus presentation and before saccade initiation were analyzed. The initial visual response of frontal eye field neurons was modulated by the presence of multiple stimuli and by whether a saccade was going to be pro-duced, but the initial visual response did not discriminate the target of the search array from the distracters. In the latent period before saccade initiation, the activity of most

The influential “premotor theory of attention” proposes that developing oculomotor commands mediate covert visual spatial attention. A likely source of this attentional bias is the frontal eye field (FEF), an area of the frontal cortex involved in converting visual information into saccade commands. We investigated the link between FEF activity and covert spatial attention by recording from FEF visual and saccade-related neurons in monkeys performing covert visual search tasks without eye movements. Here we show that the source of attention signals in the FEF is enhanced activity of visually responsive neurons. At the time attention is allocated to the visual search target, nonvisually responsive saccade-related movement neurons are inhibited. Therefore, in the FEF, spatial attention signals are independent of explicit saccade command signals. We propose that spatially selective activity in FEF visually responsive neurons corresponds to the mental spotlight of attention via modulation of ongoing visual processing.

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Population vectors were used to examine information represented by a population of prefrontal activity and its temporal change during spatial working memory processes while monkeys performed ODR and R-ODR tasks. In the ODR task, monkeys made a saccade to the cue location after the delay, whereas in the R-ODR task, they made a saccade 90 ° clockwise from the cue location. We first constructed population vectors using cue- and response-period activity. The directions of population vectors were similar to the cue directions and the saccade target directions, respectively, indicating that population vectors correctly represented information regarding directions of visual cues and saccade targets. We then calculated population vectors during a 250 ms time-window from the cue presentation to the end of the response period. In the ODR task, all population vectors were directed toward the cue direction. However, in the R-ODR task, the population vector gradually rotated during the delay period from the cue direction to the saccade direction. These results indicate that spatial information represented by a population of prefrontal activity can be shown as the direction of the population vector and that its temporal change during spatial working memory tasks can be depicted as the temporal change of the vector’s direction.

To examine the role of three cortical eye fields during internally guided decision-making processes, we recorded neuronal activities in the frontal eye field (FEF), supplementary eye field (SEF), and lateral intraparietal cortex (LIP) using a free-choice delayed saccade task with two synchronized targets. Although the monkeys must perform the task in a time-locked manner, they were free to choose either the receptive field (RF) target or the nonreceptive field (nRF) target to receive reward. In all three areas we found neurons with stronger activation during trials when the monkey was going to make a saccade to the RF target (RF trials) than to the nRF target (nRF trials). Modulation occurred not only during target presentation (visual bias) but also before target presentation (anticipatory bias). The visual bias was evident as an attenuated visual response to the RF stimulus in nRF trials. The anticipatory bias, however, was seen Many areas of the primate brain contribute to the generation and control of saccadic eye movements. At least three areas in the monkey cerebral cortex are thought to participate actively in saccade initiation: the frontal eye field (FEF) (Bruce and Goldberg, 1985), the supplementary eye field (SEF) (Schlag and Schlag-Rey, 1987), and the lateral intraparietal cortex (LIP) (Andersen and Gnadt, 1989). Neurons in these areas are not only active before and during saccades but also respond to visual targets (Mohler et al., 1973; Goldberg and Bushnell, 1981; Schall, 1991b; Colby et al., 1996). All three of these cortical eye fields also project to the superior colliculus (SC) where saccadic or gaze

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Generating sequences of multiple saccadic eye movements allows us to search our environment quickly and efficiently. Although the frontal eye field cortex (FEF) has been linked to target selection and making saccades, little is known about its role in the control and performance of the sequences of saccades made during self-guided visual search. We recorded from FEF cells while monkeys searched for a target embedded in natural scenes, and examined the degree to which cells with visual and visuo-movement activity showed evidence of target selection for future saccades. We found that for about half of these cells, activity during the fixation period between saccades predicted the next saccade in a sequence at an early time that precluded selection based upon current visual input to a cell’s response field. In addition to predicting the next saccade, activity during the fixation prior to two successive saccades also predicted the direction and goal of the second saccade in the sequence. We refer to this as advanced predictive activity. Unlike activity indicating the upcoming saccade, advanced predictive activity occurred later in the fixation period, mirroring the order of the saccade sequence itself. The remaining