Receptive Fields In Area Research Articles

Spatiotemporal integration of isolated binocular three-dimensional motion cues

Two primary binocular cues—based on velocities seen by the two eyes or on temporal changes in binocular disparity—support the perception of three-dimensional (3D) motion. Although these cues support 3D motion perception in different perceptual tasks or regimes, stimulus cross-cue contamination and/or substantial differences in spatiotemporal structure have complicated interpretations. We introduce novel psychophysical stimuli which cleanly isolate the cues, based on a design introduced in oculomotor work (Sheliga, Quaia, FitzGibbon, & Cumming, 2016). We then use these stimuli to characterize and compare the temporal and spatial integration properties of velocity- and disparity-based mechanisms. On average, temporal integration of velocity-based cues progressed more than twice as quickly as disparity-based cues; performance in each pure-cue condition saturated at approximately 200 ms and approximately 500 ms, respectively. This temporal distinction suggests that disparity-based 3D direction judgments may include a post-sensory stage involving additional integration time in some observers, whereas velocity-based judgments are rapid and seem to be more purely sensory in nature. Thus, these two binocular mechanisms appear to support 3D motion perception with distinct temporal properties, reflecting differential mixtures of sensory and decision contributions. Spatial integration profiles for the two mechanisms were similar, and on the scale of receptive fields in area MT. Consistent with prior work, there were substantial individual differences, which we interpret as both sensory and cognitive variations across subjects, further clarifying the case for distinct sets of both cue-specific sensory and cognitive mechanisms. The pure-cue stimuli presented here lay the groundwork for further investigations of velocity- and disparity-based contributions to 3D motion perception.

Stimulus-dependent modulations of correlated high-frequency oscillations in cat visual cortex.

The hypothesis that correlated neural activity is involved in the cortical representation of visual stimuli was examined by recording multi-unit activity and local field potentials from neurons with non-overlapping receptive fields in areas 17 and 18. Using coherence functions, correlations of oscillatory patterns (35-100 Hz) of neural signals were investigated under three stimulus conditions: (i) a whole field grating or a long bar moving across both receptive fields; (ii) masking the region between both receptive fields while stimulating the remaining visual field; and (iii) two separate stimuli simultaneously moving in opposite directions. Coherences of oscillations were found to be significantly higher in the first stimulus condition than in the other two conditions. Since different visual stimuli were reflected in the coherence of neural activity, we concluded that correlated neural activity is a potential candidate for coding of sensory information.

Stimulus dependent intercolumnar synchronization of single unit responses in cat area 17.

Recent concepts of cortical information processing suggest that visual stimuli are represented by ensembles of synchronously firing neurones. This hypothesis predicts that individual cells in separate columns of the visual cortex should synchronize their discharges in response to a single coherent stimulus and fire asynchronously when each neurone responds to a different stimulus. To test this prediction, we recorded simultaneously with two stereotrodes from single units with non-overlapping, colinearly arranged receptive fields in area 17 of the anaesthetized cat. In support of the hypothesis, cell pairs activated by the same long bar stimulus discharged in synchrony, and fired with no or diminished temporal correlation when each neurone was activated by an independent light bar.

The organization of receptive fields in area 18 neurones of the cat varies with the spatio-temporal characteristics of the visual stimulus

The spatial frequency tuning curves of neurones of area 18 depend upon the velocity of the visual stimulus. The higher the velocity the lower the spatial frequencies to which the cell is tuned. Since in area 17 the size of the cell receptive field is inversely related with the optimal spatial frequency to which the cell responds, we have investigated whether the shift of the optimal spatial frequency with the velocity corresponds to a "change" in the receptive field size. We recorded extracellularly from neurones in area 18; for each cell we selected two gratings, one of high spatial frequency drifting at low velocity and another of low spatial frequency drifting at high velocity to which the cell gave comparable responses. The results show that the masking of the cells receptive field which abolishes the response to the high frequency low velocity grating does not prevent the cell from responding to the low frequency high velocity grating. We conclude that the size of the receptive field of neurones in area 18 depends upon the characteristics (spatial frequency and velocity) of the visual stimulus.

Cardiac sympathetic afferent input onto neurons in nucleus ventralis posterolateralis in cat thalamus

Neurons receiving cardiac sympathetic afferent input were studied in the nucleus ventralis posterolateralis (VPL) of the cat thalamus. Animals were anesthetized with urethan-chloralose. Units in the VPL were classified into 3 classes; low-threshold mechanoreceptive (LTM), nociceptive specific (NS) and wide dynamic range (WRD) units. Units driven by electrical stimulation of the left inferior cardiac nerve (ICN) were not included in the population of LTM units, but 43.5% of NS units and 68.8% of WDR units were excited by this stimulation. Units exclusively responsive to caridiac sympathetic afferents were found. Both NS and WDR units were located in the shell region of the caudal VPL. NS units responsive to cardiac afferents had a circumscribed cutaneous receptive field in the area corresponding to tactile dermatomes C 5–T 13. WDR units receiving cardiac sympathetic afferent input had at least a part of their receptive fields in the same area. These results thatthe shell region of the caudal VPL constitutes a thalamic link in a cardiac pain pathway, and that cardiac and cutaneous pain systems share a common projection locus in the VPL.

Retinal constraints on orientation specificity in cat visual cortex

Most retinal ganglion cells (Levick and Thibos, 1982) and cortical cells (Leventhal, 1983; Leventhal et al., 1984) subserving peripheral vision respond best to stimuli that are oriented radially, i.e., like the spokes of a wheel with the area centralis at the hub. We have extended this work by comparing directly the distributions of orientations represented in topographically corresponding regions of retina and visual cortex. Both central and peripheral regions were studied. The relations between the orientations of neighboring ganglion cells and the manner in which the overrepresentation of radial orientations is accommodated in the functional architecture of visual cortex were also studied. Our results are based on an analysis of the orientations of the dendritic fields of 1296 ganglion cells throughout the retina and the preferred orientations of 1389 cells located in retinotopically corresponding regions of cortical areas 17, 18, and 19 in the cat. We find that horizontal and vertical orientations are overrepresented in regions of both retina and visual cortex subserving the central 5 degrees of vision. The distributions of the orientations of retinal ganglion cells and cortical cells subserving the horizontal, vertical, and diagonal meridians outside the area centralis differ significantly. The distribution of the preferred orientations of the S (simple) cells in areas 17, 18 and 19 subserving a given part of the retina corresponds to the distribution of the dendritic field orientations of the ganglion cells in that part of retina. The distribution of the preferred orientations of C (complex) cells with narrow receptive fields in area 17 but not C cells with wide receptive fields in areas 17, 18, or 19 subserving a given part of the retina matches the distribution of the orientations of the ganglion cells in that part of retina. The orientations of all of the alpha-cells in 5-9 mm2 patches of retina along the horizontal, vertical, and oblique meridians were determined. A comparison of the orientations of neighboring cells indicates that other than a mutual tendency to be oriented radially, ganglion cells with similar orientations are not clustered in the retina. Reconstructions of electrode penetrations into regions of visual cortex representing peripheral retina indicate that columns subserving radial orientations are wider than those subserving nonradial orientations. Our results provide evidence that the distribution of the preferred orientations of simple cells in visual cortex subserving any region of the visual field matches the distribution of the orientations of the ganglion cells subserving the same region of the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

Interhemispheric influences on area 19 of the cat.

Anatomical studies have shown an extensive network of homotopic and heterotopic interhemispheric connections in area 19 of the cat visual cortex (Segraves and Rosenquist 1982a; 1982b). We have investigated their functional organization by recording visual responses in area 19 of cats following a midsagittal section of the optic chiasm. This operation interrupts all crossed optic fibers coming both from the nasal and the temporal retinae; as a result, each hemisphere receives optic fibers only from the lateral hemiretina of the ipsilateral eye which conveys information from the contralateral visual field. Visual information transmitted to the same hemisphere from the contralateral retina and the ipsilateral visual field must be attributed to an indirect, interhemispheric pathway. We found that a rather high proportion of neurons (31.8%) in area 19 of seven split-chiasm cats responded to visual stimuli presented to the contralateral eye. All neurons receiving this interhemispheric activation were also driven by the ipsilateral eye via an intrahemispheric pathway. The property of binocularity was significantly related to the visuotopic map in that both receptive fields of each binocular neuron adjoined or were in the immediate vicinity of the vertical meridian. Due to the small size of receptive fields in area 19, the contribution of the interhemispheric pathway to the representation of the visual field is rather limited and it is certainly less extensive than that predicted by anatomical studies. The representation of the ipsilateral visual field in area 19 of intact cats, as assessed electrophysiologically, was comparable to that found in split-chiasm cats. Recordings in areas 17-18 of split-chiasm cats showed that the visual field represented through the corpus callosum in these visual areas is certainly not less and probably more, extensive than that found in area 19. The results support the conclusion that the relation to the vertical meridian and the receptive field size can explain the organization of the interhemispheric connections in the visual areas studied so far.

Responses of thalamic and hypothalamic neurons to scrotal warming in rats: Non-specific responses?

Activities of thalamic and hypothalamic neurons in response to scrotal temperature change were investigated in urethanized (1.2–1.5 g/kg) rats with special attention to changes in cortical electroencephalogram (EEG). Somatosensory relay neurons were identified electrophysiologically in the ventrobasal complex (VB) of the thalamus. These neurons had tactile receptive fields in areas outside the scrotum. Forty out of 44 of these neurons responded to scrotal warming by increase in firing rate. The responses occurred abruptly at threshold temperatures ranging from 31 to 40 °C (switching response) with simultaneous changes in EEG from high to low voltages (desynchronization). In both the thalamus and the hypothalamus, neurons excited or inhibited by scrotal warming were also excited or inhibited, respectively, by noxious stimulation that produced EEG desynchronization. Neurons showing no response to scrotal warming were not affected by noxious stimulation. In deeply anesthetized (2.5 g/kg urethane) rats, VB relay neurons responded to tactile stimulation of their receptive fields, but scrotal warming produced no change in either EEG or activities of thalamic and hypothalamic neurons. These facts suggest that the responses of thalamic and hypothalamic neurons to scrotal warming may be ‘non-specific’. Most thalamic and hypothalamic neurons showing switching responses did not appear to mediate specific information concerning scrotal skin temperature.

Linear and non-linear properties of simple and complex receptive fields in area 17 of the cat visual cortex. A model of the field.

Responses of neurones in area 17 of the cat visual cortex to gratings with sinusoidal distribution of luminance were studied. Impulse responses of the simple fields were found to be modulated by gratings passing the field. The complex fields proved to be of three types: with modulated responses, unmodulated responses, and with modulated responses against unmodulated background. Amplitudephase characteristic measured were inverse Fourier transformed to obtain the field's weighting function. Simultaneously the amplitude-phase characteristic was reconstructed from the weighting function from the responses to edges and bars, with the use of the Fourier transform. Cross-comparison of the reconstructed amplitudephase characteristics and the weighting functions showed that a receptive field has some linear properties but, strictly considered, is a non-linear system. Simple fields display the largest degree of linearity. The weighting function of a simple field does practically not depend on the stimulus velocity. At lowest velocities, however, there additional waves in the weighting function can appear, which results in a narrower bandwidth. The higher the complexity of the field that is to say the greater the number of subfields of the preceding level are, the greater are the deviations from linearity until it is completely lost in some complex fields with the unmodulated type of response. As linear methods are inadequate for dealing with cortical receptive fields, their qualitative identification was performed in model experiments on a computer. A model was fitted to observations by varying the parameters of the model for a receptive field, such as the number and weights of subfields, the extent of their spatial overlap, the time constant of excitatory and inhibitory processes and detection level. The evidence obtained suggest that the receptive fields of the visual cortex form a system of operators which perform the expansion of the image on non-classical pattern. Such an expansion can be termed a piecewise quasi-Fourierdescription. Although receptive fields of the visual cortex have been studied in a great number of investigations, the properties of the fields as described by linear analysis are as yet imperfectly understood. In the present paper we have studied responses of simple and complex receptive fields in area 17 of the cat visual cortex to moving gratings of different spacial frequency with sinusoidal distribution of luminance. The amplitudephase characteristics obtained were inverse Fourier transformed, and the weighting functions reconstructed were compared with the weighting functions obtrined from responses to bars or edges moved through the field. In a similar manner, the weighting function obtained from the responses to bars or edges were Fourier transformed and the corresponding frequency characteristics were compared with those experimentally obtained. Such cross-comparison allowed us to make estimates of linear and non-linear properties of a field to reveal sources of non-linearity. Based on these results we propose a model of the field and discuss a possible role of the field in processing of visual information.