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Science. 1992 Feb 28;255(5048):1141-3.
Form-cue invariant motion processing in primate visual cortex. Albright TD. Salk Institute for Biological Studies, La Jolla, CA 92186. |
The direction and rate at which an object moves are normally not correlated with
the manifold physical cues (for example, brightness and texture) that enable it to be seen. As befits its goals, human perception of visual motion largely evades this diversity of cues for image form; direction and rate of motion are perceived (with few exceptions) in a fashion that does not depend on the physical characteristics of the object. The middle temporal visual area of the primate cerebral cortex contains many neurons that respond selectively to motion in a particular direction and is an integral part of the neural substrate for perception of motion. When stimulated with moving patterns characterized by one of three very diverse cues for form, many middle temporal neurons exhibited similar directional tuning. This lack of sensitivity for figural cue characteristics may allow the uniform perception of motion of objects having a broad spectrum of physical cues. |
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Vis Neurosci. 1989;2(2):177-88.
Centrifugal directional bias in the middle temporal visual area (MT) of the macaque. Albright TD. Department of Psychology, Princeton University. |
We have examined the distribution of preferred directions of motion for neurons
in the middle temporal visual area (MT) of the macaque. We found a marked anisotropy favoring directions that are oriented away from the center of gaze. This anisotropy is present only among neurons with peripherally located receptive fields. This peripheral centrifugal directionality bias corresponds well to the biased distribution of motions characteristic of optic flow fields, which are generated by displacement of the visual world during forward locomotion. The bias may facilitate the processing of this common form of visual stimulation and could underlie previously observed perceptual anisotropies favoring centrifugal motion. We suggest that the bias could arise from exposure of modifiable cortical circuitry to a naturally occurring form of selective visual experience. |
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Exp Brain Res. 1987;65(3):582-92.
Local precision of visuotopic organization in the middle temporal area (MT) of the macaque. Albright TD, Desimone R. |
The representation of the visual field in the middle temporal area (MT) was
examined by recording from single neurons in anesthetized, immobilized macaques. Measurements of receptive field size, variability of receptive field position (scatter) and magnification factor were obtained within the representation of the central 25 degree. Over at least short distances (less than 3 mm), the visual field representation in MT is surprisingly orderly. Receptive field size increases as a linear function of eccentricity and is about ten times larger than in V1 at all eccentricities. Scatter in receptive field position at any point in the visual field representation is equal to about one-third of the receptive field size at that location, the same relationship that has been found in V1. Magnification factor in MT is only about one-fifth that reported in V1 within the central 5 degree but appears to decline somewhat less steeply than in V1 with increasing eccentricity. Because the smaller magnification factor in MT relative to V1 is complemented by larger receptive field size and scatter, the point-image size (the diameter of the region of cortex activated by a single point in the visual field) is roughly comparable in the two areas. On the basis of these results, as well as on our previous finding that 180 degrees of axis of stimulus motion in MT are represented in about the same amount of tissue as 180 degrees of stimulus orientation in V1, we suggest that a stimulus at one point in the visual field activates at least as many functional "modules" in MT as in V1. |
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J Neurophysiol. 1984 Dec;52(6):1106-30.
Direction and orientation selectivity of neurons in visual area MT of the macaque. Albright TD. |
We recorded from single neurons in the middle temporal visual area (MT) of the
macaque monkey and studied their direction and orientation selectivity. We also recorded from single striate cortex (V1) neurons in order to make direct comparisons with our observations in area MT. All animals were immobilized and anesthetized with nitrous oxide. Direction selectivity of 110 MT neurons was studied with three types of moving stimuli: slits, single spots, and random-dot fields. All of the MT neurons were found to be directionally selective using one or more of these stimuli. MT neurons exhibited a broad range of direction-tuning bandwidths to all stimuli (minimum = 32 degrees, maximum = 186 degrees, mean = 95 degrees). On average, responses were strongly unidirectional and of similar magnitude for all three stimulus types. Orientation selectivity of 89 MT neurons was studied with stationary flashed slits. Eighty-three percent were found to be orientation selective. Overall, orientation-tuning bandwidths were significantly narrower (mean = 64 degrees) than direction-tuning bandwidths for moving stimuli. Moreover, responses to stationary-oriented stimuli were generally smaller than those to moving stimuli. Direction selectivity of 55 V1 neurons was studied with moving slits; orientation selectivity of 52 V1 neurons was studied with stationary flashed slits. In V1, compared with MT, direction-tuning bandwidths were narrower (mean = 68 degrees). Moreover, V1 responses to moving stimuli were weaker, and bidirectional tuning was more common. The mean orientation-tuning bandwidth in V1 was also significantly narrower than that in MT (mean = 52 degrees), but the responses to stationary-oriented stimuli were of similar magnitude in the two areas. We examined the relationship between optimal direction and optimal orientation for MT neurons and found that 61% had an orientation preference nearly perpendicular to the preferred direction of motion, as is the case for all V1 neurons. However, another 29% of MT neurons had an orientation preference roughly parallel to the preferred direction. These observations, when considered together with recent reports claiming sensitivity of some MT neurons to moving visual patterns (39), suggest specific neural mechanisms underlying pattern-motion sensitivity in area MT. These results support the notion that area MT represents a further specialization over area V1 for stimulus motion processing. Furthermore, the marked similarities between direction and orientation tuning in area MT in macaque and owl monkey support the suggestion that these areas are homologues. |
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J Neurophysiol. 1984 Jan;51(1):16-31.
Columnar organization of directionally selective cells in visual area MT of the macaque. Albright TD, Desimone R, Gross CG. |
We recorded from single neurons in visual area MT of the macaque in order to
examine the spatial distribution of its directionally selective cells. The animals were paralyzed and anesthetized with nitrous oxide. All MT neurons (n = 614) responded better to moving stimuli than to stationary stimuli. For 55% of the neurons, responses to moving stimuli were independent of stimulus color, shape, length, or orientation. For the remaining cells, stimulus length affected the response magnitude and tuning bandwidth but not the preferred direction. MT neurons were divided into four categories on the basis of their sensitivity to moving stimuli: 60% responded exclusively to one direction of motion, 24% responded best to one direction with a weaker response in the opposite direction, 8% responded equally well to two opposite directions of motion, and 8% responded equally well to all directions of motion. The direction preferences of successively sampled cells on a penetration either changed by small increments or occasionally by approximately 180 degrees. Thus, there is a systematic representation of direction of motion. The representation of axis of motion, i.e., the orientation of the path along which a stimulus moves, is more continuous than the representation of direction of motion. There was a systematic relationship between penetration angle and rate of change of preferred axis of motion, indicating that cells with a similar axis of motion preference are arranged in vertical columns. Furthermore, axis of motion columns appear to exist in the form of continuous slabs in area MT. The size of these slabs is such that 180 degrees of axis of motion are represented in 400-500 micron of cortex. There was also a systematic relationship between penetration angle and frequency of 180 degrees reversals, indicating that cells with a similar direction of motion preference are also organized in vertical columns and cells with opposite direction preferences are located in adjacent columns within a single axis of motion column. Just as in macaque striate cortex where approximately 500 micron of cortex contain the mechanism for the local analysis of stimulus orientation, so in MT approximately 500 micron of cortex contain the mechanism for the local analysis of stimulus motion. |
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J Cogn Neurosci. 2004 May;16(4):521-7.
Direct current stimulation over V5 enhances visuomotor coordination by improving motion perception in humans. Antal A, Nitsche MA, Kruse W, Kincses TZ, Hoffmann KP, Paulus W. Department of Clinical Neurophysiology, Georg-August University of Gottingen, Goettingen, Germany. AAntal@gwdg.de |
The primary aim of this study was to determine the extent to which human MT+/V5,
an extrastriate visual area known to mediate motion processing, is involved in visuomotor coordination. To pursue this we increased or decreased the excitability of MT+/V5, primary motor, and primary visual cortex by the application of 7 min of anodal and cathodal transcranial direct current stimulation (tDCS) in healthy human subjects while they were performing a visuomotor tracking task involving hand movements. The percentage of correct tracking movements increased specifically during and immediately after cathodal stimulation, which decreases cortical excitability, only when V5 was stimulated. None of the other stimulation conditions affected visuomotor performance. We propose that the improvement in performance caused by cathodal tDCS of V5 is due to a focusing effect on to the complex motion perception conditions involved in this task. This hypothesis was proven by additional experiments: Testing simple and complex motion perception in dot kinetograms, we found that a diminution in excitability induced by cathodal stimulation improved the subject's perception of the direction of the coherent motion only if this was presented among random dots (complex motion perception), and worsened it if only one motion direction was presented (simple movement perception). Our data suggest that area V5 is critically involved in complex motion perception and identification processes important for visuomotor coordination. The results also raise the possibility of the usefulness of tDCS in rehabilitation strategies for neurological patients with visuomotor disorders. |
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J Neurosci. 2001 Mar 1;21(5):1676-97.
Correlated firing in macaque visual area MT: time scales and relationship to behavior. Bair W, Zohary E, Newsome WT. Howard Hughes Medical Institute (HHMI), Center for Neural Science, New York University, New York, New York 10003, USA. wyeth@cns.nyu.edu |
We studied the simultaneous activity of pairs of neurons recorded with a single
electrode in visual cortical area MT while monkeys performed a direction discrimination task. Previously, we reported the strength of interneuronal correlation of spike count on the time scale of the behavioral epoch (2 sec) and noted its potential impact on signal pooling (Zohary et al., 1994). We have now examined correlation at longer and shorter time scales and found that pair-wise cross-correlation was predominantly short term (10-100 msec). Narrow, central peaks in the spike train cross-correlograms were largely responsible for correlated spike counts on the time scale of the behavioral epoch. Longer-term (many seconds to minutes) changes in the responsiveness of single neurons were observed in auto-correlations; however, these slow changes in time were on average uncorrelated between neurons. Knowledge of the limited time scale of correlation allowed the derivation of a more efficient metric for spike count correlation based on spike timing information, and it also revealed a potential relative advantage of larger neuronal pools for shorter integration times. Finally, correlation did not depend on the presence of the visual stimulus or the behavioral choice of the animal. It varied little with stimulus condition but was stronger between neurons with similar direction tuning curves. Taken together, our results strengthen the view that common input, common stimulus selectivity, and common noise are tightly linked in functioning cortical circuits. |
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J Neurosci. 2004 Aug 18;24(33):7305-23.
Adaptive temporal integration of motion in direction-selective neurons in macaque visual cortex. Bair W, Movshon JA. Center for Neural Science, New York University, New York, New York 10003, USA. wyeth.bair@physiol.ox.ac.uk |
Direction-selective neurons in the primary visual cortex (V1) and the
extrastriate motion area MT/V5 constitute a critical channel that links early cortical mechanisms of spatiotemporal integration to downstream signals that underlie motion perception. We studied how temporal integration in direction-selective cells depends on speed, spatial frequency (SF), and contrast using randomly moving sinusoidal gratings and spike-triggered average (STA) analysis. The window of temporal integration revealed by the STAs varied substantially with stimulus parameters, extending farther back in time for slow motion, high SF, and low contrast. At low speeds and high SF, STA peaks were larger, indicating that a single spike often conveyed more information about the stimulus under conditions in which the mean firing rate was very low. The observed trends were similar in V1 and MT and offer a physiological correlate for a large body of psychophysical data on temporal integration. We applied the same visual stimuli to a model of motion detection based on oriented linear filters (a motion energy model) that incorporated an integrate-and-fire mechanism and found that it did not account for the neuronal data. Our results show that cortical motion processing in V1 and in MT is highly nonlinear and stimulus dependent. They cast considerable doubt on the ability of simple oriented filter models to account for the output of direction-selective neurons in a general manner. Finally, they suggest that spike rate tuning functions may miss important aspects of the neural coding of motion for stimulus conditions that evoke low firing rates. |
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J Neurosci. 2002 Apr 15;22(8):3189-205.
The timing of response onset and offset in macaque visual neurons. Bair W, Cavanaugh JR, Smith MA, Movshon JA. Howard Hughes Medical Institute and Center for Neural Science, New York University, New York, New York 10003, USA. wyeth@cns.nyu.edu |
We used fast, pseudorandom temporal sequences of preferred and antipreferred
stimuli to drive neuronal firing rates rapidly between minimal and maximal across the visual system. Stimuli were tailored to the preferences of cells recorded in the lateral geniculate nucleus (magnocellular and parvocellular), primary visual cortex (simple and complex), and the extrastriate motion area MT. We found that cells took longer to turn on (to increase their firing rate) than to turn off (to reduce their rate). The latency difference (onset minus offset) varied from several to tens of milliseconds across cell type and stimulus class and was correlated with spontaneous or driven firing rates for most cell classes. The delay for response onset depended on the nature of the stimulus present before the preferred stimulus appeared, and may result from persistent inhibition caused by antipreferred stimuli or from suppression that followed the offset of the preferred stimulus. The onset delay showed three distinct types of dependence on the temporal sequence of stimuli across classes of cells, implying that suppression may accumulate or wear off with time. Onset latency is generally longer, can be more variable, and has marked stimulus dependence compared with offset latency. This suggests an important role for offset latency in assessing the speed of information transmission in the visual system and raises the possibility that signal offsets provide a timing reference for visual processing. We discuss the origin of the delay in onset latency compared with offset latency and consider how it may limit the utility of certain feedforward circuits. |
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J Neurophysiol. 1981 Mar;45(3):397-416.
Visual response properties of neurons in four extrastriate visual areas of the owl monkey (Aotus trivirgatus): a quantitative comparison of medial, dorsomedial, dorsolateral, and middle temporal areas. Baker JF, Petersen SE, Newsome WT, Allman JM. |
The response properties of 354 single neurons in the medial (M), dorsomedial
(DM), dorsolateral (DL), and middle temporal (MT) visual areas were studied quantitatively with bar, spot, and random-dot stimuli in chronically implanted owl monkeys with fixed gaze. 2. A directionality index was computed to compare the responses to stimuli in the optimal direction with the responses to the opposing direction of movement. The greater the difference between opposing directions, the higher the index. MT cells had much higher direction indices to moving bars than cells in DL, DM, and M. 3. A tuning index was computed for each cell to compare the responses to bars moving in the optimal direction, or flashed in the optimal orientation, with the responses in other directions or orientations within +/- 90 degrees. Cells in all four areas were more sharply tuned to the orientation of stationary flashed bars than to moving bars, although a few cells (9/92( were unresponsive in the absence of movement. DM cells tended to be more sharply tuned to moving bars than cells in the other areas. 4. Directionality in DM, DL, and MT was relatively unaffected by the use of single-spot stimuli instead of bars; tuning in all four areas was broader to spots than bars. 5. Moving arrays of randomly spaced spots were more strongly excitatory than bar stimuli for many neurons in MT (16/31 cells). These random-dot stimuli were also effective in M, but evoked no response or weak responses from most cells in DM and DL. 6. The best velocities of movement were usually in the range of 10-100 degrees/s, although a few cells (22/227), primarily in MT (14/69 cells), preferred higher velocities. 7. Receptive fields of neurons in all four areas were much larger than striate receptive fields. Eccentricity was positively correlated with receptive-field size (r = 0.62), but was not correlated with directionality index, tuning index, or best velocity. 8. The results support the hypothesis that there are specializations of function among the cortical visual areas. |