Contrast Dependence of Suppressive Influences in Cortical Area MT of Alert Macaque

2005 ◽  
Vol 93 (3) ◽  
pp. 1809-1815 ◽  
Author(s):  
Christopher C. Pack ◽  
J. Nicholas Hunter ◽  
Richard T. Born
Keyword(s):  
High Contrast ◽  
Area Mt ◽  
Visual Neurons ◽  
Temporal Area ◽  
Low Contrast ◽  
Information Theoretic ◽  
Tuning Curves ◽  
Mt Neurons ◽  
Moving Stimuli ◽  
High Stimulus

Visual neurons are often characterized in terms of their tuning for various stimulus properties, such as shape, color, and velocity. Generally, these tuning curves are further modulated by the overall intensity of the stimulus, such that increasing the contrast increases the firing rate, up to some maximum. In this paper, we describe the tuning of neurons in the middle temporal area (MT or V5) of macaque visual cortex for moving stimuli of varying contrast. We find that, for some MT neurons, tuning curves for stimulus direction, speed, and size are shaped in part by suppressive influences that are present at high stimulus contrast but weak or nonexistent at low contrast. For most neurons, the suppression is direction-specific and strongest for large, slow-moving stimuli. The surprising consequence of this phenomenon is that some MT neurons actually fire more vigorously to a large low-contrast stimulus than to one of high contrast. These results are consistent with recent perceptual observations, as well as with information-theoretic models, which hypothesize that the visual system seeks to reduce redundancy at high contrast while maintaining sensitivity at low contrast.

scholarly journals Misperceptions of speed are accounted for by the responses of neurons in macaque cortical area MT

2011 ◽  
Vol 105 (3) ◽  
pp. 1199-1211 ◽  
Author(s):  
Pınar Boyraz ◽  
Stefan Treue
Keyword(s):  
Human Subjects ◽  
General Mechanism ◽  
Physiological Data ◽  
Neural Basis ◽  
Area Mt ◽  
Temporal Area ◽  
Tuning Curves ◽  
Mt Neurons ◽  
Random Dot Patterns ◽  
Perceived Speed

In humans, the perceived speed of random dot patterns (RDP) moving within small apertures is faster than that of RDPs moving within larger apertures at the same physical speed. To investigate the neural basis of this illusion, we recorded the responses of direction- and speed-selective neurons in the middle temporal area (MT) of macaque monkeys to stimuli varying in size and speed. Our results show that the preferred speed of MT neurons is slower for smaller stimuli. This effect was larger for neurons preferring faster speeds, matching our psychophysical observation in human subjects that the magnitude of the misperception is larger at higher stimulus speeds. Our physiological data indicate that, across a population of speed-tuned neurons in MT, decreasing the size of a stimulus would shift the activity profile to neurons tuned for higher speeds. Modeling a labeled-line readout of this shifted profile, we show an increased apparent speed, in line with the psychophysical observations. This link strengthens the evidence for a causal role of area MT in speed perception. The systematic shift in tuning curves of single neurons with stimulus size might reflect a general mechanism for feature-mismatch illusions in visual perception.

scholarly journals Feature attention for binocular disparity in primate area MT depends on tuning strength

2015 ◽  
Vol 113 (5) ◽  
pp. 1545-1555 ◽  
Author(s):  
Douglas A. Ruff ◽  
Richard T. Born
Keyword(s):  
Binocular Disparity ◽  
Receptive Fields ◽  
Sensory Information ◽  
Neuronal Population ◽  
Area Mt ◽  
Temporal Area ◽  
Mt Neurons ◽  
Feature Attention ◽  
The Difference ◽  
The Relationship

Attending to a stimulus modulates the responses of sensory neurons that represent features of that stimulus, a phenomenon named “feature attention.” For example, attending to a stimulus containing upward motion enhances the responses of upward-preferring direction-selective neurons in the middle temporal area (MT) and suppresses the responses of downward-preferring neurons, even when the attended stimulus is outside of the spatial receptive fields of the recorded neurons (Treue S, Martinez-Trujillo JC. Nature 399: 575–579, 1999). This modulation renders the representation of sensory information across a neuronal population more selective for the features present in the attended stimulus (Martinez-Trujillo JC, Treue S. Curr Biol 14: 744–751, 2004). We hypothesized that if feature attention modulates neurons according to their tuning preferences, it should also be sensitive to their tuning strength, which is the magnitude of the difference in responses to preferred and null stimuli. We measured how the effects of feature attention on MT neurons in rhesus monkeys ( Macaca mulatta) depended on the relationship between features—in our case, direction of motion and binocular disparity—of the attended stimulus and a neuron's tuning for those features. We found that, as for direction, attention to stimuli containing binocular disparity cues modulated the responses of MT neurons and that the magnitude of the modulation depended on both a neuron's tuning preferences and its tuning strength. Our results suggest that modulation by feature attention may depend not just on which features a neuron represents but also on how well the neuron represents those features.

scholarly journals The locus of flicker adaptation in the migraine visual system: A dichoptic study

Cephalalgia ◽  
2012 ◽  
Vol 33 (1) ◽  
pp. 5-19 ◽  
Author(s):  
Michel Thabet ◽  
Frances Wilkinson ◽  
Hugh R Wilson ◽  
Olivera Karanovic
Keyword(s):  
Visual System ◽  
Interocular Transfer ◽  
Neural Model ◽  
Inhibitory Neurons ◽  
High Contrast ◽  
Low Contrast ◽  
Full Field ◽  
Dichoptic Viewing ◽  
High Stimulus ◽  
And Control

Background Flickering light has been shown to sensitize the migraine visual system at high stimulus contrast while elevating thresholds at low contrast. The present study employs a dichoptic psychophysical paradigm to ask whether the abnormal adaptation to flicker in migraine occurs before or after the binocular combination of inputs from the two eyes in the visual cortex. Methods Following adaptation to high contrast flicker presented to one eye only, flicker contrast increment thresholds were measured in each eye separately using dichoptic viewing. Results Modest interocular transfer of adaptation was seen in both migraine and control groups at low contrast. Sensitization at high contrast in migraine relative to control participants was seen in the adapted eye only, and an unanticipated threshold elevation occurred in the non-adapted eye. Migraineurs also showed significantly lower aversion thresholds to full field flicker than control participants, but aversion scores and increment thresholds were not correlated. Conclusions The results are simulated with a three-stage neural model of adaptation that points to strong adaptation at monocular sites prior to binocular combination, and weaker adaptation at the level of cortical binocular neurons. The sensitization at high contrast in migraine is proposed to result from stronger adaptation of inhibitory neurons, which act as a monocular normalization pool.

Direction and orientation selectivity of neurons in visual area MT of the macaque

1984 ◽  
Vol 52 (6) ◽  
pp. 1106-1130 ◽  
Author(s):  
T. D. Albright
Keyword(s):  
Direction Selectivity ◽  
Orientation Selectivity ◽  
Orientation Tuning ◽  
Area Mt ◽  
Mt Neurons ◽  
V1 Neurons ◽  
Moving Stimuli ◽  
Preferred Direction ◽  
Visual Area Mt ◽  
Direction Tuning

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.

Microstimulation of Cortical Area MT Affects Performance on a Visual Working Memory Task

2001 ◽  
Vol 85 (1) ◽  
pp. 187-196 ◽  
Author(s):  
James W. Bisley ◽  
Daniel Zaksas ◽  
Tatiana Pasternak
Keyword(s):  
Working Memory ◽  
Visual Motion ◽  
Memory Task ◽  
Stimulus Motion ◽  
Area Mt ◽  
Directional Information ◽  
Temporal Area ◽  
Mt Neurons ◽  
Directional Motion ◽  
Term Storage

We applied electrical stimulation to physiologically identified sites in macaque middle temporal area (MT) to examine its role in short-term storage of recently encoded information about stimulus motion. We used a behavioral task in which monkeys compared the directions of two moving random-dot stimuli, sample and test, separated by a 1.5-s delay. Four sample directions were used for each site, and the animals had to indicate whether the direction of motion in the sample was the same as or different to the direction of motion in the test. We found that the effect of stimulation of the same directional column in MT depended on the behavioral state of the animal. Although stimulation had strong effects when applied during the encoding and the storage components of the task, these effects were not equivalent. Stimulation applied during the presentation of the sample produced signals interpreted by the monkeys as directional motion. However, the same stimulation introduced during the period of storage no longer produced signals interpreted as unambiguous directional information. We conclude that the directional information used by the monkeys in the working memory task is likely to be provided by neurons in MT, and the use of this information appears to be dependent on the portion of the task during which stimulation was delivered. Finally, the disruptive effects of stimulation during the delay suggest that MT neurons not only participate in the encoding of visual motion information but also in its storage by either maintaining an active connection with the circuitry involved in storage or being an integral component of that circuitry.

scholarly journals Population Anisotropy in Area MT Explains a Perceptual Difference Between Near and Far Disparity Motion Segmentation

2011 ◽  
Vol 105 (1) ◽  
pp. 200-208 ◽  
Author(s):  
Finnegan J. Calabro ◽  
Lucia M. Vaina
Keyword(s):  
Visual Cues ◽  
Visual Motion ◽  
Population Distribution ◽  
Normal Population ◽  
Motion Processing ◽  
Area Mt ◽  
Temporal Area ◽  
Motion Discrimination ◽  
Mt Neurons ◽  
Simulated Performance

Segmentation of the visual scene into relevant object components is a fundamental process for successfully interacting with our surroundings. Many visual cues, including motion and binocular disparity, support segmentation, yet the mechanisms using these cues are unclear. We used a psychophysical motion discrimination task in which noise dots were displaced in depth to investigate the role of segmentation through disparity cues in visual motion stimuli ( experiment 1). We found a subtle, but significant, bias indicating that near disparity noise disrupted the segmentation of motion more than equidistant far disparity noise. A control experiment showed that the near-far difference could not be attributed to attention ( experiment 2). To account for the near-far bias, we constructed a biologically constrained model using recordings from neurons in the middle temporal area (MT) to simulate human observers' performance on experiment 1. Performance of the model of MT neurons showed a near-disparity skew similar to that shown by human observers. To isolate the cause of the skew, we simulated performance of a model containing units derived from properties of MT neurons, using phase-modulated Gabor disparity tuning. Using a skewed-normal population distribution of preferred disparities, the model reproduced the elevated motion discrimination thresholds for near-disparity noise, whereas a skewed-normal population of phases (creating individually asymmetric units) did not lead to any performance skew. Results from the model suggest that the properties of neurons in area MT are computationally sufficient to perform disparity segmentation during motion processing and produce similar disparity biases as those produced by human observers.

Columnar organization of directionally selective cells in visual area MT of the macaque

1984 ◽  
Vol 51 (1) ◽  
pp. 16-31 ◽  
Author(s):  
T. D. Albright ◽  
R. Desimone ◽  
C. G. Gross
Keyword(s):  
Opposite Direction ◽  
Rate Of Change ◽  
Visual Area ◽  
Local Analysis ◽  
Stimulus Motion ◽  
Area Mt ◽  
Systematic Relationship ◽  
Mt Neurons ◽  
Moving Stimuli ◽  
Visual Area Mt

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.

scholarly journals Altered sensitivity to motion of area MT neurons following long-term V1 lesions

2017 ◽  
Author(s):  
Maureen A. Hagan ◽  
Tristan A. Chaplin ◽  
Krystel R. Huxlin ◽  
Marcello G. P. Rosa ◽  
Leo L. Lui
Keyword(s):  
Striate Cortex ◽  
Clinical Work ◽  
Neuronal Responses ◽  
Area Mt ◽  
Temporal Area ◽  
Mt Neurons ◽  
Functional Implications ◽  
Thalamic Projections ◽  
Altered Sensitivity

AbstractThe middle temporal area (MT) receives its main afferents from the striate cortex (V1). However, MT also receives direct thalamic projections, which have been hypothesized to play a crucial role in residual vision after V1 lesions. MT neurons continue to respond shortly after V1 lesions, but human clinical work has shown that lesion effects can take up to six months to stabilize, making it important to understand MT responses after long-term deprivation of V1 inputs. We recorded neuronal responses in MT to moving dot stimuli in adult marmoset monkeys, 7-11 months after unilateral V1 lesions. Fewer MT neurons were direction selective, including neurons whose locations corresponded to the intact parts of V1. Firing rates were higher and more variable, and increased with motion strength regardless of direction. These properties could be re-created by a network model with imbalanced inhibition and excitation, providing the first insights into functional implications of long-term plasticity in MT following V1 lesions.

scholarly journals Attention improves information flow between neuronal populations without changing the communication subspace

2021 ◽  
Author(s):  
Ramanujan Srinath ◽  
Douglas A Ruff ◽  
Marlene R Cohen
Keyword(s):  
Decision Making ◽  
Visual Attention ◽  
Visual Information ◽  
Receptive Fields ◽  
Perceptual Decision Making ◽  
Visual Neurons ◽  
Temporal Area ◽  
Mt Neurons ◽  
Neuronal Populations ◽  
Oculomotor Neurons

Visual attention allows observers to flexibly use or ignore visual information, suggesting that information can be flexibly routed between visual cortex and neurons involved in decision-making. We investigated the neural substrate of flexible information routing by analyzing the activity of populations of visual neurons in the medial temporal area (MT) and oculomotor neurons in the superior colliculus (SC) while rhesus monkeys switched spatial attention. We demonstrated that attention increases the efficacy of visuomotor communication: trial-to-trial variability of the population of SC neurons was better predicted by the activity of MT neurons (and vice versa) when attention was directed toward their joint receptive fields. Surprisingly, this improvement in prediction was not explained or accompanied by changes in the dimensionality of the shared subspace or in local or shared pairwise noise correlations. These results suggest a mechanism by which visual attention can affect perceptual decision-making without altering local neuronal representations.

scholarly journals Altered Sensitivity to Motion of Area MT Neurons Following Long-Term V1 Lesions

2019 ◽  
Vol 30 (2) ◽  
pp. 451-464 ◽  
Author(s):  
Maureen A Hagan ◽  
Tristan A Chaplin ◽  
Krystel R Huxlin ◽  
Marcello G P Rosa ◽  
Leo L Lui
Keyword(s):  
Neural Responses ◽  
Neuronal Responses ◽  
Area Mt ◽  
Temporal Area ◽  
Motion Sensitivity ◽  
Firing Rates ◽  
Mt Neurons ◽  
Residual Motion ◽  
Altered Sensitivity

Abstract Primates with primary visual cortex (V1) damage often retain residual motion sensitivity, which is hypothesized to be mediated by middle temporal area (MT). MT neurons continue to respond to stimuli shortly after V1 lesions; however, experimental and clinical studies of lesion-induced plasticity have shown that lesion effects can take several months to stabilize. It is unknown what physiological changes occur in MT and whether neural responses persist long after V1 damage. We recorded neuronal responses in MT to moving dot patterns in adult marmoset monkeys 6–12 months after unilateral V1 lesions. In contrast to results obtained shortly after V1 lesions, we found that fewer MT neurons were direction selective, including neurons expected to still receive projections from remaining parts of V1. The firing rates of most cells increased with increases in motion strength, regardless of stimulus direction. Furthermore, firing rates were higher and more variable than in control MT cells. To test whether these observations could be mechanistically explained by underlying changes in neural circuitry, we created a network model of MT. We found that a local imbalance of inhibition and excitation explained the observed firing rate changes. These results provide the first insights into functional implications of long-term plasticity in MT following V1 lesions.

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