Chromatic subclasses of frog retinal ganglion cells: studies using black stimuli moving on a monochromatic background.
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Animals↗
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Direction asymmetry by moving stimuli and static receptive field plots for simple cells in cat striate cortex.
It has been suggested that direction asymmetry of simple cells by moving stimuli is due to asymmetries in flanking response regions in the receptive field, and that the stronger response in the preferred direction is caused by synchronized On- and Off-responses. The hypothesis was tested by comparing the response of direction asymmetric cells to moving and static stimuli. The hypothesis had a weak but statistically significant predictive power. However, both for cells where the predicted preferred direction was correct and where it was wrong, there was clear suppression of the response in the nonpreferred movement direction, indicating that direction asymmetry is due to inhibitory processes rather than to synchronized On and Off-responses. It is suggested that the asymmetries in flanking regions of static receptive field plots are caused by the same inhibition which produces direction asymmetry, thus explaining why the static plots have some predictive power on direction asymmetry.
Animals↗
Chromatic properties of the retinal afferents in the thalamus and the tectum of the frog (Rana temporaria).
In order to clarify physiological mechanisms underlying colour-specific visually guided behaviour, we measured spectral sensitivities of On-fibres projecting to the thalamus and class 2 and 3 fibres passing to tectum opticum. In addition we recorded responses of these fibres to moving coloured papers with known spectral reflectancies. The latter method, here called paper colourimetry, allowed us to change the relative stimulations of the blue-, green- and red-sensitive photoreceptors in any direction desired. Under the photopic conditions used the tectal fibres were driven exclusively by red-sensitive receptors, while the thalamic fibres received strong On-inputs from both red- and blue-sensitive receptors. Due to a partly antagonistic interaction between these inputs the On-fibres acted in a dichromatic way, responding with specific extended low-frequency discharges to all relative increases in blue receptor stimulation, e.g. to a great reduction in red stimulation combined with unchanged blue stimulation. Thus they have functional characteristics which could serve a visual system showing colour constancy.
Action Potentials↗
Neural interactions of two moving patterns in the direction and orientation domain in the complex cells of cat's visual cortex.
An examination was made of the responses of complex cells in cat's striate cortex to a textured (nonoriented) stimulus moving in the preferred direction, superimposed upon either a textured or a grating stimulus (oriented) that was moved in different directions. The cell discharges elicited by the textured stimulus moving in the preferred direction were reduced by the textured stimulus moving in nonpreferred directions, and increased when moved in the preferred direction. A grating moving in nonpreferred directions showed similar inhibitory effects on the responses to a textured stimulus moving in the preferred direction. Neural processing for directional movement is, therefore, affected by other neural processing for directional movement, and still more by that for orientation.
Animals↗
Measuring the spatial frequency selectivity of second-order texture mechanisms.
Recent investigations of texture and motion perception suggest two early filtering stages: an initial stage of selective linear filtering followed by rectification and a second stage of linear filtering. Here we demonstrate that there are differently scaled second-stage filters, and we measure their contrast modulation sensitivity as a function of spatial frequency. Our stimuli are Gabor modulations of a suprathreshold, bandlimited, isotropic carrier noise. The subjects' task is to discriminate between two possible orientations of the Gabor. Carrier noises are filtered into four octave-wide bands, centered at m = 2, 4, 8, and 16 c/deg. The Gabor test signals are w = 0.5, 1, 2, 4 and 8 c/deg. The threshold modulation of the test signal is measured for all 20 combinations of m and w. For each carrier frequency m, the Gabor test frequency w to which subjects are maximally sensitive appears to be approximately 3-4 octaves below m. The consistent m x w interaction suggests that each second-stage spatial filter may be differentially tuned to a particular first-stage spatial frequency. The most sensitive combination is a second-stage filter of 1 c/deg with first-stage inputs of 8-16 c/deg. We conclude that second-order texture perception appears to utilize multiple channels tuned to spatial frequency and orientation, with channels tuned to low modulation frequencies appearing to be best served by carrier frequencies 8 to 16 times higher than the modulations they are tuned to detect.
Contrast Sensitivity↗
The difference between the perception of absolute and relative motion: a reaction time study.
We used a reaction-time paradigm to examine the extent to which motion detection depends on relative motion. In the absence of relative motion, the responses could be described by a simple model based on the detection of a fixed change in position. If relative motion was present, the responses could be modelled using characteristics of motion detectors. Comparing reaction times when relative and absolute velocity are equal with ones when relative velocity is twice the absolute velocity reveals that these detectors measure relative motion.
Humans↗
Nausogenic properties of various dynamic and static force environments.
Motion sickness can occur when an accelerating force acting on the human body repeatedly changes amplitude and direction or both. It also can occur without any motion after transfer into a constant force field significantly different from Earth-gravity. Dynamic and static causes of motion sickness can be distinguished accordingly. Space sickness, too, has dynamic as well as static aspects. Dynamic space sickness might depend on increased bilateral differential sensitivity of the peripheral and central vestibular apparatus, whereas static space sickness may be caused by erroneous compensation of bilaterial asymmetries of the otolith-system in the microgravity environment. Experiments in airplanes, cars and on a vestibular sled have shown that the susceptibility to motion sickness is highest for changes of acceleration in the negative X-axis (as compared to the other axes) of the body. During reciprocating linear accelerations on the vestibular sled, standstill periods of movement and the direction of movement cannot correctly be indicated, because the peripheral vestibular apparatus lacks true motion detectors.
Acceleration↗
Effect of the richness of the environment on neurons in cat visual cortex. II. Spatial and temporal frequency characteristics.
The quantitative distribution of synaptic contacts in the cat cerebral cortex is affected by the richness of the environment: the number of round-asymmetrical (RA) synapses per neuron is higher while the number of flat-symmetrical (FS) contacts is lower in the visual cortex of cats raised in an enriched environmental condition (EC) compared to those reared in an impoverished condition (IC). The size of FS synaptic contacts is also affected by the complexity of the animal's environment. It has been suggested that these morphological synaptic changes induced by the richness of the environment correlate with differences in physiological properties of the visual cortex. This question has been explored by assessing the cortical unit contrast sensitivity as a function of spatial and temporal frequency of area 17 cells in cats raised either in isolation (IC) or in a colony with ample environmental stimulation (EC). Contrast sensitivity is affected by the richness of the environment: at the preferred spatial frequency, an average enriched unit can detect lower contrasts (mean = 0.6%) than an average impoverished cell (0.9%; P less than 0.002). In addition, the mean highest spatial frequency that can be resolved (acuity) is greater in EC than in IC cells (1.7 and 1.2 cycles per degree, respectively, P less than 0.0001), whereas the spatial frequency at which units respond best is not statistically affected by the environment. The preferred temporal frequency also show a significant difference in EC (1.0-6.5 Hz) and IC units (0.9-4.0 Hz; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Iso- and cross-oriented columns in cat striate cortex: a study with simultaneous single- and multi-unit recordings.
The constancy of orientation tuning in vertical columns of the visual cortex of the cat was examined with conventional and newly developed multi-electrode methods. Preferred orientation was measured with single- and multi-unit recordings in 68 penetrations approximately perpendicular to the cortical layers and with inter-recording steps of only 40-70 microns. The tuning curves obtained revealed three types of penetration sequences: no-shift penetrations (37%), one-shift penetrations (41%) and double-shift penetrations (22%). Particular attention was paid to the orientation tuning at the transition zones below layer IV. The use of the multi-unit recording technique enabled the measurement of cross-oriented activity within a single electrode position mostly around the border between layers IV and V. Altering the type of anaesthesia (ventilation with room air or nitrous oxide-oxygen) produced only a quantitative change in the percentage of the encountered penetration types. The results suggest that upper and lower layers follow different principles of functional organization. As a consequence different types of columns, especially iso- and cross-oriented ones, are produced in a systematic way.
Animals↗
The cerebellum as a predictor of neural messages--II. Role in motor control and motion sickness.
The hypothesis of a "stable estimator" was proposed in the preceding article as a circuit computing an internal estimate of a body movement variable and endowed with regulating properties. Such a circuit would exist for each variable, and would be embedded in a particular folium of the cerebellar cortex and the related paths of the brainstem nuclei and the inferior olive. In this article, the action of the premotor orders on the stable estimator circuit is studied, at initiation and during execution of voluntary movements. A feedback loop via the cerebellar cortex would control on-going movements and maintain the efficacy of the stabilizing sensorimotor reaction, while preventing its interfering with the movement. The regulating loop via the inferior olive would have a short-term role in initiating movements and would boost insufficient stabilizing reactions. The discrepancy between internal estimates of the same variable would be reflected in motion sickness.
Cerebellum↗
Is perceived angular displacement the time integral of perceived angular velocity?
Estimates of rotational self-displacement and self-velocity have been used interchangeably in vestibular psycho-physics to characterize vestibular ego-motion perception. However, the assumption underlying this indiscriminate use has never been tested. The assumption holds that the two estimates are equivalent, with the displacement estimates reflecting the time integral of the signal underlying the velocity estimate. We tested this hypothesis by directly comparing displacement and velocity estimates. Two groups of healthy young subjects (2 x n = 15) were presented with the same vestibular stimuli (horizontal whole body rotations in the dark in the form of velocity steps of 5, 10, 20, and 40 degrees/s with 1, 2, 4, 8, and 16 s duration, yielding position ramps of 5, 10, 20, 40, 80, 160, and 320 degrees total displacement). The first subject group estimated peak velocity, and the second group estimated total displacement, both groups using a comparable psychophysical procedure (Stevens' magnitude estimation). The experimentally obtained velocity estimates were used to predict the displacement estimates. To this end, the velocity signal was assumed to decay exponentially from the reported peak value (reflecting the dynamics of peripheral and early central vestibular mechanisms) and was mathematically integrated. Predicted and measured displacement estimates were similar when a time constant of 20 s was assumed, which is in good agreement with earlier studies. We conclude that vestibular displacement estimates can, indeed, be considered equivalent to vestibular velocity estimates, at least for the stimulus parameters used.
Adult↗
Motion sickness preceded by unstable displacements of the center of pressure.
We exposed standing participants to optic flow in a moving room. Motion sickness was induced by motion that simulated the amplitude and frequency of standing sway. We identified instabilities in displacements of the center of pressure among participants who became sick; these instabilities occurred before the onset of subjective motion sickness symptoms. Postural differences between Sick and Well participants were observed before exposure to the nauseogenic stimulus. During exposure to the nauseogenic stimulus, sway increased for participants who became sick but also for those who did not. However, at every point during exposure sway was greater for participants who became motion sick. The results reveal that motion sickness is preceded by instabilities in displacements of the center of pressure.
Adaptation, Physiological↗
Motion sickness is linked to nystagmus-related trigeminal brain stem input: a new hypothesis.
Motion sickness is a common and distressing but poorly understood syndrome associated with nausea/vomiting and autonomic nervous system accompaniments that develops in the air or space as well as on sea or land. A bidirectional aetiologic link prevails between migraine and motion-sickness. Motion sickness provokes jerk nystagmus induced by both optokinetic and vestibular stimulation. Fixation of gaze or closure of eyes generally prevents motion sickness while vestibular otolithic function is eliminated in microgravity of space, indicating a predominant pathogenetic role for visuo-sensory input. Scopolamine, dimenhydrinate, and promethazine reduce motion-related nystagmus. Contraction of extraocular muscles generates proprioceptive neural traffic and can provoke an ocular hypertensive response. It is proposed that repetitive contractions of the extraocular muscles during motion-related jerk nystagmus rapidly augment brain stem afferent input by increasing proprioceptive neural traffic through connections of the oculomotor nerves with the ophthalmic nerve in the lateral wall of the cavernous sinus as well as by raising the intraocular pressure thereby stimulating anterior segment ocular trigeminal nerve fibers. This verifiable hypothesis defines the pathophysiological basis of individual susceptibility to motion sickness, elucidates the preventive mechanism of gaze fixation or ocular closure, advances the aetiologic link between MS and migraine, rationalizes the mechanism of known preventive drugs, and explores new therapeutic possibilities.
Afferent Pathways↗
Effects of immersion in virtual reality on postural control.
In the present study, we examined the effects of the time lag between visual scene and the head movement in the virtual reality (VR) world on motion sickness and postural control in healthy volunteers. After immersion in VR with additional time lags (from 0 to 0.8 s) to the inherent delay (about 250 ms), the visual-vestibular conflict induced a slight motion sickness in experimental subjects, but no change was noticed in the body sway path with eyes open and closed. However, Romberg ratio of body sway path with eyes closed divided by that with eyes open after immersion in VR was significantly decreased in comparison with that before immersion in VR. Since Romberg ratio is an index of visual dependency on postural control, this finding indicates that the immersion in VR decreases the visual dependency on postural control. It is suggested that adaptation to visual-vestibular conflict in VR immersion increases the contribution of vestibular and somatosensory inputs to postural control by ignoring the conflicting delayed visual input in the VR world. VR may be a promising treatment for visual vertigo in vestibular patients with unsuccessful compensation by its ability to induce vestibular and somatosensory reweighing for postural control.
Adult↗
Hemispheric integration and differences in perception of a line-motion illusion in the divided brain.
Five people lacking the corpus callosum (two callosotomized, three with agenesis of the corpus callosum) and neurologically normal subjects were shown vertical lines that appeared instantaneously between pairs of rectangles in one or other visual field. When one of the rectangles flashed prior to the presentation of the line, and the line was in the same visual field, all subjects perceived the line as spreading from the flashed rectangle to the other. Normal subjects and one of the callosotomized subjects showed a slight but significant right visual-field advantage, perhaps reflecting a left-hemispheric superiority in processing rapid temporal events. The illusion was also induced when the line and the flash were in opposite visual fields in one of the callosotomized, one of the acallosal subjects, and about half of the normal subjects, implying interhemispheric integration even in the absence of the corpus callosum.
Adult↗
Spatial and temporal visual properties of single neurons in the suprageniculate nucleus of the thalamus.
The spatial and temporal visual sensitivity to drifting sinusoidal gratings was studied in 105 neurons of the suprageniculate nucleus of the feline thalamus. Extracellular single-unit recordings were performed in halothane-anesthetized, immobilized, artificially ventilated cats. Most suprageniculate nucleus cells were strongly sensitive to the direction of drifting gratings. The suprageniculate nucleus units had a clear preference for very low spatial frequencies with a mean of 0.05 cycle/deg. The spatial resolution was also very low with a mean of 0.16 cycle/deg. Most of the cells displayed low-pass spatial tuning characteristics, while the remainder of the units were band-pass tuned. The suprageniculate nucleus units were extremely narrowly tuned, to spatial frequencies with a mean spatial bandwidth of 1.07 octaves. A majority of the units responded optimally to high temporal frequencies, with a mean of 8.53 Hz. The temporal frequency tuning functions predominantly revealed a band-pass character, with a mean temporal bandwidth of 1.66 octaves. These results demonstrate that the neurons in the suprageniculate nucleus display particular spatial and temporal characteristics. The spatial and temporal tuning properties of the suprageniculate nucleus neurons are very similar to those of the superior colliculus and the anterior ectosylvian cortex, structures that provide the main visual afferentation toward the suprageniculate nucleus. This suggests their common function in motion perception, and especially in the recording of movements of the visual environment relative to the body, and the related behavioral action.
Animals↗
Always returning: feedback and sensory processing in visual cortex and thalamus.
Feedback projections are an integral part of the mammalian visual system. Although it is tempting to relegate them to a subsidiary role in visual processing, because their supposed latency and lag might appear to be unfavourable for an involvement in fast processing, this is a dangerous simplification. Certainly for the world in motion, feedback from higher motion areas can influence the transfer of ascending input when, or even before, the input arrives. Here, we consider the circuit formed by layer 6 feedback cells in the visual cortex and how this straddles the retinothalamic and thalamocortical transfer of visual input. We discuss its links to feedback from the cortical motion area MT (V5), and suggest that motion perception involves a dynamic interplay between MT, V1 and the thalamus. This review is part of the TINS special issue on The Neural Substrates of Cognition.
Animals↗
Level and mechanisms of perceptual learning: learning first-order luminance and second-order texture objects.
Perceptual learning is an improvement in perceptual task performance reflecting plasticity in the perceptual system. Practice effects were studied in two object orientation tasks: a first order, luminance object task and a second-order, texture object task. Perceptual learning was small or absent in the first-order task, but consistently occurred for the second-order (texture) task, where it was limited to improvements in low external noise conditions, or stimulus enhancement [Dosher, B., & Lu, Z. -L. (1998). Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting. Proceedings of the National Academy of Sciences of the United States of America, 95 (23) 13988-13993; Dosher, B., & Lu, Z. -L. (1999). Mechanisms of perceptual learning. Vision Research, 39 (19) 3197-3221], analogous to attention effects in first- and second-order motion processing [Lu, Z. -L., Liu, C. Q., & Dosher, B. (2000). Attention mechanisms for multi-location first- and second-order motion perception. Vision Research, 40 (2) 173-186]. Perceptual learning affected the later, post-rectification, stages of perceptual analysis, possibly localized at V2 or above. It serves to amplify the stimulus relative to limiting internal noise for intrinsically noisy representations of second-order stimuli.
Attention↗