Mass-action view of single-cell responses to stimulation of the receptive field and/or beyond: exemplification with data from the rabbit primary visual cortex

Whereas single cells in the visual cortex prefer moving light bars, mass-action responses are evoked better by diffuse luminance changes. This discrepancy was investigated by quantitatively comparing the the response properties of individual cells with those a representative group of cells. The latter responses were derived from the single-cell responses, which were obtained from recording in the rabbit. These quantitative estimates of mean responses resolve the discrepancy between the single-cell domain and the mass-action domain: from the single-cell point of view, a properly oriented moving-bar stimulus is much more effective than a diffuse-light stimulus. The corresponding mass-action response to one common moving-bar stimulus, however, is as small as the mean response to a diffuse-light stimulus (which may even be presented at retinotopically non-corresponding sites). The peak intensities of these mass responses are even much stronger with the diffuse-light stimuli. The same conclusions are valid for the cat, as could be verified from published data. The restrictions of the local receptive field concept that may be implied by the mass-action view of cortical activity and the potential functional relevance of mass activities area discussed.     

Primary visual cortex activity along the apparent-motion trace reflects illusory perception

The illusion of apparent motion can be induced when visual stimuli are successively presented at different locations. It has been shown in previous studies that motion-sensitive regions in extrastriate cortex are relevant for the processing of apparent motion, but it is unclear whether primary visual cortex (V1) is also involved in the representation of the illusory motion path. We investigated, in human subjects, apparent-motion-related activity in patches of V1 representing locations along the path of illusory stimulus motion using functional magnetic resonance imaging. Here we show that apparent motion caused a blood-oxygenation-level-dependent response along the V1 representations of the apparent-motion path, including regions that were not directly activated by the apparent-motion-inducing stimuli. This response was unaltered when participants had to perform an attention-demanding task that diverted their attention away from the stimulus. With a bistable motion quartet, we confirmed that the activity was related to the conscious perception of movement. Our data suggest that V1 is part of the network that represents the illusory path of apparent motion. The activation in V1 can be explained either by lateral interactions within V1 or by feedback mechanisms from higher visual areas, especially the motion-sensitive human MT/V5 complex.     

Competition-integration of blue and orange stimuli in Halobacterium salinarum cannot occur solely in SRI photoreceptor

Experiments on the integration of blue and orange stimuli in Halobacterium salinarum were performed by using different combinations of blue and orange steps. The results show that the prevalence of the blue stimulus over the orange one depends on both the blue and the orange light intensities. A quantitative analysis of the current hypotheses on the phototransduction of orange and UV-blue light stimuli is presented, showing that the balancing between the two antagonistic stimuli should depend only on the intensity of the blue stimulus and not on that of the orange one, provided that the combination of the two stimuli occurs linearly at the photoreceptor stage. We conclude that blue and orange stimuli elicit distinct intracellular signals whose integration occurs downstream of the photoreceptor.     

Sensitization and habituation of the swimming behavior in ascidian larvae to light

Ascidian larvae of Ciona intestinalis change their photic behavior during the course of development. Newly hatched larvae show no response to a light stimulus at any intensity. At 4 hr after hatching, larvae were induced to start to swimming upon the cessation of illumination, and to stop swimming upon the onset of illumination. At a weaker light intensity (5.0 x 10(-3) J/m (2).s), the larvae showed similar responses to either a single stimulus or repeated stimuli of onset and cessation of light until 10 hr after hatching. At a stronger light intensity (3.2 x 10(-1) J/m(2).s), when the stimulus was repeated, they showed sensitization and habituation of the swimming response. At 3 hr after hatching the larvae failed to show any response to an initial stimulus at any intensity of light, but after several repeated stimuli (sensitization) they showed a swimming response at light intensities above 4.0 x 10(-2) J/m (2).s. At 5 hr and with intensity above 1.0 x 10 (-2) J/m(2).s, the larvae showed photoresponses to the first stimulus, but after several repetitions the larvae failed to stop swimming upon the onset of light (habituation). A repeated series of stimuli at stronger intensities of light caused greater habituation; this habituation was retained for about 1 min. Since the larval central nervous system in Ciona is comprised of only about 100 neurons, learning behavior in ascidian larvae should provide insights for a minimal mechanism of memory in vertebrates.     

Influence of Visual Motion,Suggestion, and Illusory Motion on Self-Motion Perception in the Horizontal Plane

A moving visual field can induce the feeling of self-motion or vection. Illusory motion from static repeated asymmetric patterns creates a compelling visual motion stimulus, but it is unclear if such illusory motion can induce a feeling of self-motion or alter self-motion perception. In these experiments, human subjects reported the perceived direction of self-motion for sway translation and yaw rotation at the end of a period of viewing set visual stimuli coordinated with varying inertial stimuli. This tested the hypothesis that illusory visual motion would influence self-motion perception in the horizontal plane. Trials were arranged into 5 blocks based on stimulus type: moving star field with yaw rotation, moving star field with sway translation, illusory motion with yaw, illusory motion with sway, and static arrows with sway. Static arrows were used to evaluate the effect of cognitive suggestion on self-motion perception. Each trial had a control condition; the illusory motion controls were altered versions of the experimental image, which removed the illusory motion effect. For the moving visual stimulus, controls were carried out in a dark room. With the arrow visual stimulus, controls were a gray screen. In blocks containing a visual stimulus there was an 8s viewing interval with the inertial stimulus occurring over the final 1s. This allowed measurement of the visual illusion perception using objective methods. When no visual stimulus was present, only the 1s motion stimulus was presented. Eight women and five men (mean age 37) participated. To assess for a shift in self-motion perception, the effect of each visual stimulus on the self-motion stimulus (cm/s) at which subjects were equally likely to report motion in either direction was measured. Significant effects were seen for moving star fields for both translation (p = 0.001) and rotation (p<0.001), and arrows (p = 0.02). For the visual motion stimuli, inertial motion perception was shifted in the direction consistent with the visual stimulus. Arrows had a small effect on self-motion perception driven by a minority of subjects. There was no significant effect of illusory motion on self-motion perception for either translation or rotation (p>0.1 for both). Thus, although a true moving visual field can induce self-motion, results of this study show that illusory motion does not.     

Moving Stimuli Are Less Effectively Masked Using Traditional Continuous Flash Suppression (CFS) Compared to a Moving Mondrian Mask (MMM): A Test Case for Feature-Selective Suppression and Retinotopic Adaptation

Continuous flash suppression (CFS) is a powerful interocular suppression technique, which is often described as an effective means to reliably suppress stimuli from visual awareness. Suppression through CFS has been assumed to depend upon a reduction in (retinotopically specific) neural adaptation caused by the continual updating of the contents of the visual input to one eye. In this study, we started from the observation that suppressing a moving stimulus through CFS appeared to be more effective when using a mask that was actually more prone to retinotopically specific neural adaptation, but in which the properties of the mask were more similar to those of the to-be-suppressed stimulus. In two experiments, we find that using a moving Mondrian mask (i.e., one that includes motion) is more effective in suppressing a moving stimulus than a regular CFS mask. The observed pattern of results cannot be explained by a simple simulation that computes the degree of retinotopically specific neural adaptation over time, suggesting that this kind of neural adaptation does not play a large role in predicting the differences between conditions in this context. We also find some evidence consistent with the idea that the most effective CFS mask is the one that matches the properties (speed) of the suppressed stimulus. These results question the general importance of retinotopically specific neural adaptation in CFS, and potentially help to explain an implicit trend in the literature to adapt one’s CFS mask to match one’s to-be-suppressed stimuli. Finally, the results should help to guide the methodological development of future research where continuous suppression of moving stimuli is desired.     

Representation of moving stimuli by somatosensory neurons.

The findings obtained in neurophysiological and psychophysical investigations using tactile stimuli that move at constant velocity across the skin are reviewed. For certain neurons in the postcentral gyrus of the cerebral cortex (S-I) of macaque monkeys, direction of stimulus motion is a "trigger feature" i.e., moving tactile stimuli evoke vigorous discharge activity in these neurons only if the stimuli are moved in a particular direction across the receptive field. This directional selectivity is maximal when stimulus velocity is between 5 and 50 cm/sec, and falls off rapidly at lower or higher velocities. The capacity for human subjects to correctly identify the direction of stimulus motion on the skin exhibits a similar dependence on stimulus velocity. The similar effects of velocity on neural and psychophysical measures of directional sensitivity support the idea that direction of stimulus motion on the skin can only be recognized if the moving stimulus optimally activates the group of S-I neurons for which that directions of simulus motion is the trigger feature.     

Contextual modulation of V1 receptive fields depends on their spatial symmetry

The apparent receptive field characteristics of sensory neurons depend on the statistics of the stimulus ensemble—a nonlinear phenomenon often called contextual modulation. Since visual cortical receptive fields determined from simple stimuli typically do not predict responses to complex stimuli, understanding contextual modulation is crucial to understanding responses to natural scenes. To analyze contextual modulation, we examined how apparent receptive fields differ for two stimulus ensembles that are matched in first- and second-order statistics, but differ in their feature content: one ensemble is enriched in elongated contours. To identify systematic trends across the neural population, we used a multidimensional scaling method, the Procrustes transformation. We found that contextual modulation of receptive field components increases with their spatial extent. More surprisingly, we also found that odd-symmetric components change systematically, but even-symmetric components do not. This symmetry dependence suggests that contextual modulation is driven by oriented On/Off dyads, i.e., modulation of the strength of intracortically-generated signals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Accession of sweet stimuli to receptors. I. Absolute dominance of one molecular species in binary mixtures

Intensity/time studies of sweetness response in pure solutions of each of nine different sweet stimuli have been carried out. Both variables exhibit simple power functions of the form Intensity (S) = kscns and Persistence (P) = kpcnp. In binary mixtures of these nine stimuli a depression (or negative synergism) of both sweetness intensity and persistence is observed which is predictable from the low exponents of the power functions. Combination of both power functions allows the "effective concentration" of each stimulus in a binary mixture to be calculated from its observed intensity/time characteristics. All "effective concentrations" calculable in this way show absolute dominance of one stimulus in mixtures of two irrespective of the relative proportions of the two stimuli. It is suggested that the "effective concentrations" may reflect real concentrations of a single molecular species in the microenvironment of the receptor. Thus the accession of sweet molecules to ordered, localized concentrations at the receptor is ultimately dependent on chemical structure.     

Visual processing levels revealed by response latencies to changes in different visual attributes.

Visual latencies, and their variation with stimulus attributes, can provide information about the level in the visual system at which different attributes of the image are analysed, and decisions about them made. A change in the colour, structure or movement of a visual stimulus brings about a highly reproducible transient constriction of the pupil that probably depends on visual cortical mechanisms. We measured this transient response to changes in several attributes of visual stimuli, and also measured manual reaction times to the same stimulus changes. Through analysis of latencies, we hoped to establish whether changes in different stimulus attributes were processed by mechanisms at the same or different levels in the visual pathway. Pupil responses to a change in spatial structure or colour are almost identical, but both are ca. 40 ms slower than those to a change in light flux, which are thought to depend largely on subcortical pathways. Manual reaction times to a change in spatial structure or colour, or to the onset of coherent movement, differ reliably, and all are longer than the reaction time to a change in light flux. On average, observers take 184 ms to detect a change in light flux, 6 ms more to detect the onset of a grating, 30 ms more to detect a change in colour, and 37 ms more to detect the onset of coherent motion. The pattern of latency variation for pupil responses and reaction times suggests that the mechanisms that trigger the responses lie at different levels in cortex. Given our present knowledge of visual cortical organization, the long reaction time to the change in motion is surprising. The range of reaction times across different stimuli is consistent with decisions about the onset of a grating being made in V1 and decisions about the change in colour or change in motion being made in V4.     

Linear Relations between Stimulus Amplitudes and Amplitudes of Retinal Action Potentials from the Eye of the Wolf Spider

Incremental photic stimuli have been used to elicit small amplitude retinal action potentials from light-adapted ocelli of the wolf spider, Lycosa baltimoriana (Keyserling) in order to see whether or not the amplitudes of these potentials are linearly related to the stimulus amplitudes. Sine wave variations of light intensity around a mean elicit sine wave variations in potential which contain inappreciable harmonics of the stimulus frequency and whose amplitudes are linearly related to the stimulus amplitudes. Likewise, the responses to the first two periodic Fourier components of incremental rectangular wave stimuli of variable duty cycle are directly proportional to the amplitudes of these components and have phases dependent only on the frequencies and phases of these components. Thirdly, a linear transfer function can be found which describes the amplitudes and phases of responses recorded at different frequencies of sine wave stimulation and this transfer function is sufficient to predict the responses to incremental step stimuli. Finally, it is shown that flash response amplitudes are linearly related to incremental flash intensities at all levels of adaptation. The relations of these linear responses to non-linear responses and to physiological mechanisms of the eye are discussed.     

Auditory steady-state responses to multiple simultaneous stimuli

Steady-state responses can follow multiple simultaneous auditory stimuli. If the stimuli are modulated at different rates, responses specific to each stimulus can be assessed by measuring in the frequency domain response the spectral component corresponding to the rate of modulation. When each stimulus has a different carrier frequency or different ear of presentation, the responses when 8 stimuli are presented simultaneously are not significantly different than when each stimulus is presented alone. Since significant responses can be recognized down to intensities that average 14 dB above behavioral threshold, this technique may be useful in objective audiometry. It is also possible to record steady-state responses to multiple modulations of the same carrier frequency. In this case, the amplitude of the responses when the stimuli are combined is smaller than when the stimuli are presented alone. The decrease in amplitude depends upon the number of concomitant stimuli and their relative intensities. These effects are probably due to the compressive rectification occurring during cochlear transduction, and the data may be used to model cochlear processing of auditory stimuli.     

Adaptive surround modulation in cortical area MT

Visual motion perception relies on two opposing operations: integration and segmentation. Integration overcomes motion ambiguity in the visual image by spatial pooling of motion signals, whereas segmentation identifies differences between adjacent moving objects. For visual motion area MT, previous investigations have reported that stimuli in the receptive field surround, which do not elicit a response when presented alone, can nevertheless modulate responses to stimuli in the receptive field center. The directional tuning of this "surround modulation" has been found to be mainly antagonistic and hence consistent with segmentation. Here, we report that surround modulation in area MT can be either antagonistic or integrative depending upon the visual stimulus. Both types of modulation were delayed relative to response onset. Our results suggest that the dominance of antagonistic modulation in previous MT studies was due to stimulus choice and that segmentation and integration are achieved, in part, via adaptive surround modulation.     

Comparative aerial and underwater motion perception capability of the mink (Mustela vison) as a function of stimulus radiant intensity and discrimination distance

The ability of mink to discriminate the direction of a fast, horizontally moving spot of light was investigated in air and underwater, over a range of stimulus radiant intensities (25–58×10⁴ μWsteradian^?1) and using discrimination distances from 10 cm to 50 cm. Threshold results indicated broadly equivalent motion preception capability in air and underwater, until low stimulus radiant intensity became limiting, when a more marked decline in perceptual ability underwater became apparent. The effect of changing discrimination distance was investigated in terms of the concomitant change in stimulus duration and angular displacement. The results are discussed with reference to the observed predatory behaviour of mink.     

Responses of tectal neurons to contrasting stimuli: an electrophysiological study in the barn owl

The saliency of visual objects is based on the center to background contrast. Particularly objects differing in one feature from the background may be perceived as more salient. It is not clear to what extent this so called "pop-out" effect observed in humans and primates governs saliency perception in non-primates as well. In this study we searched for neural-correlates of pop-out perception in neurons located in the optic tectum of the barn owl. We measured the responses of tectal neurons to stimuli appearing within the visual receptive field, embedded in a large array of additional stimuli (the background). Responses were compared between contrasting and uniform conditions. In a contrasting condition the center was different from the background while in the uniform condition it was identical to the background. Most tectal neurons responded better to stimuli in the contrsating condition compared to the uniform condition when the contrast between center and background was the direction of motion but not when it was the orientation of a bar. Tectal neurons also preferred contrasting over uniform stimuli when the center was looming and the background receding but not when the center was receding and the background looming. Therefore, our results do not support the hypothesis that tectal neurons are sensitive to pop-out per-se. The specific sensitivity to the motion contrasting stimulus is consistent with the idea that object motion and not large field motion (e.g., self-induced motion) is coded in the neural responses of tectal neurons.     

Interaction of perceptual grouping and crossmodal temporal capture in tactile apparent-motion

Previous studies have shown that in tasks requiring participants to report the direction of apparent motion, task-irrelevant mono-beeps can "capture" visual motion perception when the beeps occur temporally close to the visual stimuli. However, the contributions of the relative timing of multimodal events and the event structure, modulating uni- and/or crossmodal perceptual grouping, remain unclear. To examine this question and extend the investigation to the tactile modality, the current experiments presented tactile two-tap apparent-motion streams, with an SOA of 400 ms between successive, left-/right-hand middle-finger taps, accompanied by task-irrelevant, non-spatial auditory stimuli. The streams were shown for 90 seconds, and participants' task was to continuously report the perceived (left- or rightward) direction of tactile motion. In Experiment 1, each tactile stimulus was paired with an auditory beep, though odd-numbered taps were paired with an asynchronous beep, with audiotactile SOAs ranging from -75 ms to 75 ms. Perceived direction of tactile motion varied systematically with audiotactile SOA, indicative of a temporal-capture effect. In Experiment 2, two audiotactile SOAs--one short (75 ms), one long (325 ms)--were compared. The long-SOA condition preserved the crossmodal event structure (so the temporal-capture dynamics should have been similar to that in Experiment 1), but both beeps now occurred temporally close to the taps on one side (even-numbered taps). The two SOAs were found to produce opposite modulations of apparent motion, indicative of an influence of crossmodal grouping. In Experiment 3, only odd-numbered, but not even-numbered, taps were paired with auditory beeps. This abolished the temporal-capture effect and, instead, a dominant percept of apparent motion from the audiotactile side to the tactile-only side was observed independently of the SOA variation. These findings suggest that asymmetric crossmodal grouping leads to an attentional modulation of apparent motion, which inhibits crossmodal temporal-capture effects.     

60 Hz electric fields and incandescent light as aversive stimuli controlling the behavior of rats responding under concurrent schedules of reinforcement

Several reports have shown that animals will sometimes engage in behaviors that reduce their exposure to a 60 Hz electric field (E-field). The field, therefore, can function as an aversive stimulus. In other studies, the E-field at equivalent strengths failed to function as an aversive stimulus. The present experiment, using rats, demonstrates how factors other than field strength can influence whether a subject engages in behavior that reduces field exposure. The general design consisted of giving the rat a choice between two alternatives, one of which sometimes included an added stimulus. Each subject was trained to press each of two levers to obtain food. Pressing one lever was reinforced intermittently under a variable interval 2 min schedule (VI 2); pressing the other lever was reinforced by a second VI 2 schedule operating independently of the first. Under this concurrent schedule the rat spent 50% of the daily 50 min session responding to each of the levers, indicating that they were equally “valued.” Next, while the schedules remained in effect, the first response to one of the levers turned on a 100 kV/m E-field which remained on until the rat pressed the other lever. The time spent responding under the schedule associated with the field was reduced by about 5–10%. When the procedure was changed so that no lever presses produced food, i.e., extinction, but the added stimulus contingency remained, the rats spent even less time in the presence of the field. Similar outcomes were observed during both the concurrent food or extinction schedules when incandescent light was used. Thus, both an E-field and incandescent light functioned as aversive stimuli, but the magnitude of the aversiveness was small. Aversiveness depended not only on stimulus intensity, but also on behavioral factors. Bioelectromagnetics 19:210–221, 1998. © 1998 Wiley-Liss, Inc.     

Quantifying human circadian pacemaker response to brief, extended, and repeated light stimuli over the phototopic range

The authors' previous models have been able to describe accurately the effects of extended (approximately 5 h) bright-light (>4000 lux) stimuli on the phase and amplitude of the human circadian pacemaker, but they are not sufficient to represent the surprising human sensitivity to both brief pulses of bright light and light of more moderate intensities. Therefore, the authors have devised a new model in which a dynamic stimulus processor (Process L) intervenes between the light stimuli and the traditional representation of the circadian pacemaker as a self-sustaining limit-cycle oscillator (Process P). The overall model incorporating Process L and Process P is intended to allow the prediction of phase shifts to photic stimuli of any temporal pattern (extended and brief light episodes) and any light intensity in the photopic range. Two time constants emerge in the Process L model: the characteristic duration for necessary bright-light pulses to achieve their full effect (5-10 min) and the characteristic stimulus-free (dark) interval that can be tolerated without incurring an excessive penalty in phase shifting (30-80 min). The effect of reducing light intensity is incorporated in Process L as an extension of the time necessary for the light pulse to be fully realized (a power-law relation between time and intensity). This new model generates a number of new testable hypotheses, including the surprising prediction that 24-h cycles consisting of 8 h of darkness and 16 h of only approximately 3.5 lux would be capable of entraining a large fraction of the adult population (approximately 45%). Experimental data on the response of the human circadian system to lower light intensities and briefer stimuli are needed to allow for further refinement and validation of the model proposed here.     

Kinematic and aerodynamic aspects of ultrasound-induced negative phonotaxis in flying Australian field crickets (Teleogryllus oceanicus)

Negative phonotaxis is elicited in flying Australian field crickets, Teleogryllus oceanicus, by ultrasonic stimuli. Using upright tethered flying crickets, we quantitatively examined several kinematic and aerodynamic factors which accompany ultrasound-induced negative phonotactic behavior. These factors included three kinematic effects (hindwing wingbeat frequency, hindwing elevation and depression, and forewing tilt) and two aerodynamic effects (pitch and roll). 1. Within two cycles following a 20 dB suprathreshold ultrasonic stimulus, the hindwing wingbeat frequency increases by 3-4 Hz and outlasts the duration of the stimulus. Moreover, the relationship between the maximum increase in wingbeat frequency and stimulus intensity is a two-stage response. At lower suprathreshold intensities the maximum wingbeat frequency increases by approximately 1 Hz; but, at higher intensities, the maximum increase is 3-4 Hz. 2. The maximum hindwing elevation angle increases on the side ipsilateral to the stimulus, while there was no change in upstroke elevation on the side contralateral to the stimulus. 3. An ultrasonic stimulus affects forewing tilt such that the forewings bank into the turn. The forewing ipsilateral to the stimulus tilts upward while the contralateral forewing tilts downward. Both the ipsilateral and contralateral forewing tilt change linearly with stimulus intensity. 4. Flying crickets pitch downward when presented with a laterally located ultrasonic stimulus. Amputation experiments indicate that both the fore and hindwings contribute to changes in pitch but the pitch response in an intact cricket exceeds the simple addition of fore and hindwing contributions. With the speaker placed above or below the flying cricket, the change is downward or upward, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulus size selectivity and receptive field organization of ectostriatal neurons in the pigeon

The avian ectostriatum is the telencephalic recipient zone of the tectofugal pathway, which may be homologous to the colliculo-pulvinar-cortical pathway in mammals. The present paper studies the visual response properties and receptive field organization of ectostriatal cells in pigeons with extracellular recording and computer mapping techniques. The results indicate that 90% of ectostriatal cells prefer forward, downward and upward motion of visual stimuli at velocities in the range of 16-128 degrees s(-1). They respond optimally to small stimuli (1-4 degrees visual angle), mostly preferring a target of 2 degrees. Most cells (78.8%) have one excitatory receptive field that usually possesses one or two hotspots, some cells (13.5%) have two excitatory receptive fields each having one or two hotspots, and a few cells (7.7%) have one excitatory receptive field with an unresponsive region in the center. An inhibitory receptive field is not found surrounding the excitatory receptive field in the ectostriatal cells examined. These response properties and receptive field organization may reflect the possible roles of the ectostriatum in stimulus discrimination and visual cognition.