Humans use saccadic eye movements to make frequent gaze changes, yet the associated full-field image motion is not perceived. The theory of saccadic suppression has been proposed to account for this phenomenon, but it is not clear whether suppression originates from a retinal signal at saccade onset or from the brain before saccade onset. Perceptually, visual sensitivity is reduced before saccades and enhanced afterward. Over the same time period, the perception of time is compressed and even inverted. We explore the origins and neural basis of these effects by recording from neurons in the dorsal medial superior temporal area (

The ectostriatum is a large visual structure in the avian telencephalon. Part of the tectofugal pathway, the ectostriatum receives a large ascending thalamic input from the nucleus rotundus, the homolog of the mammalian pulvinar complex. We investigated the effects of bilateral lesions of the ectostriatum in pigeons on visual motion and spatial-pattern perception tasks. To test motion perception, we measured performance on a task requiring detection of coherently moving random dots embedded in dynamic noise. To test spatialpattern perception, we measured performance on the detection of a square wave grating embedded in static noise. A double dissociation was revealed. Pigeons with lesions to the caudal ectostriatum showed a performance deficit on the motion task but not the grating task. In contrast, pigeons with lesions to the rostral ectostriatum showed a performance deficit on the grating task but not the motion task. Thus, in the avian telencephalon, there is a separation of visual motion and spatial-pattern perception as there is in the mammalian telencephalon. However, this separation of function is in the targets of the tectofugal pathway in pigeons rather than in the thalamofugal pathway as described in mammals. The implications of these findings with respect to the evolution of the visual system are discussed. Specifically, we suggest that the principle of parallel visual streams originated in the tectofugal pathway rather than the thalamofugal pathway.

Previous studies investigating the response properties of neurons in the primary visual cortex of cats and primates have shown that prolonged exposure to optimally oriented, high-contrast gratings leads to a reduction in responsiveness to subsequently presented test stimuli. We recorded from 119 neurons in cat V1 and V2 and found that in a high proportion of cells contrast adaptation also occurs for gratings oriented orthogonal to a neuron's preferred orientation, even though this stimulus did not elicit significant increases in spiking activity. Approximately 20% of neurons adapted equally to all orientations tested and a further 46% showed at least some adaptation to orthogonally oriented gratings, whereas 20% of neurons did not adapt to orthogonal gratings. The magnitude of contrast adaptation was positively correlated with adapting contrast, but was not related to the spiking activity of the cells. Highly direction selective neurons produced stronger adaptation to orthogonally oriented gratings than other neurons. Orientation-related adaptation was correlated with the rate of change of orientation tuning in consecutive cells along electrode penetrations that traveled parallel to the cortical layers. Nonoriented adaptation was most common in areas where orientation preference changed rapidly, whereas orientation-selective adaptation was most common in areas where orientation preference changed slowly. A minority of neurons did not show contrast adaptation (14%). No major differences were found between units in different cortical layers, V1 and V2, or between complex and simple cells. The relevance of these findings to the current understanding of adaptation within the context of orientation column architecture is discussed.

Neurons in the pretectal nucleus lentiformis mesencephali (LM) are involved in the analysis of optic flow that results from self-motion. Previous studies have shown that LM neurons have large receptive fields in the contralateral eye, are excited in response to largefield stimuli moving in a particular (preferred) direction, and are inhibited in response to motion in the opposite (anti-preferred) direction. We investigated the responses of LM neurons to sine wave gratings of varying spatial and temporal frequency drifting in the preferred and anti-preferred directions. The LM neurons fell into two categories. "Fast" neurons were maximally excited by gratings of low spatial [0.03-0.25 cycles/ degrees (cpd)] and mid-high temporal frequencies (0.5-16 Hz). "Slow" neurons were maximally excited by gratings of high spatial (0.35-2 cpd) and low-mid temporal frequencies (0.125-2 Hz). Of the slow neurons, all but one preferred forward (temporal to nasal) motion. The fast group included neurons that preferred forward, backward, upward, and downward motion. For most cells (81%), the spatial and temporal frequency that elicited maximal excitation to motion in the preferred direction did not coincide with the spatial and temporal frequency that elicited maximal inhibition to gratings moving in the anti-preferred direction. With respect to motion in the anti-preferred direction, a substantial proportion of the LM neurons (32%) showed bi-directional responses. That is, the spatiotemporal plots contained domains of excitation in addition to the region of inhibition. Neurons tuned to stimulus velocity across different spatial frequency were rare (5%), but some neurons (39%) were tuned to temporal frequency. These results are discussed in relation to previous studies of the responses of neurons in the accessory optic system and pretectum to drifting gratings and other largefield stimuli.

The responses of neurons in the middle temporal and medial superior temporal areas of macaque cortex are suppressed during saccades compared with saccade-like stimulus movements. We utilized the short-latency ocular following paradigm to show that this saccadic suppression is followed by postsaccadic enhancement of motion responses. The level of enhancement decays with a time constant of 100 ms from saccade end. The speed of ocular following is also enhanced after saccades and decays over a similar time course, suggesting a link between the neural and behavioral effects. There is some evidence that maximum postsaccadic enhancement occurs when cells are stimulated at their optimum speeds. Latencies of motion responses are saccade dependent: 37 ms for saccade-generated motion, 45 ms for motion in the half-second after saccades, and 70 ms with no prior saccades. The finding that saccades alter response latencies may partially explain perceptual time compression during saccades and time dilation after saccades.