PubMed Health⌕ Search

Biomedical subjects

S Lehmkuhle

Publications and source records attributed to S Lehmkuhle.

At least 19 recordsLinked to original sources
PubMed1998

Visually evoked cortical potentials in awake cats during saccadic eye movements.

Visually evoked potentials (VEPs) measured under conditions of retinal image stabilization that minimized the influences of visual masking and smearing were averaged from electroencephalographic records measured from striate cortex of three cats. The amplitudes of the VEPs increased around saccade initiation. The grating-evoked potentials obtained at different times relative to the saccade exhibited changes in waveform shape that could be attributed to a saccade-evoked potential. The changes in the shape of the waveform were reasonably accounted for by the summation of the grating-evoked potential (produced when the cat did not make a saccade) and an appropriately timed saccade-evoked potential. The fundamental amplitudes of the residual potentials were computed and found to vary across the time course of the saccade. These observations suggest that there are other influences besides visual masking that are exerted early in the visual pathway to modulate visual processing during saccadic eye movements. A corollary discharge process is the most likely candidate to exert these influences.

Animals↗
PubMed1997

Transient visual attention is dominated by the magnocellular stream.

Robust visual attentional responses are produced by the sudden onset of a visual cue, but the properties of cues that best elicit an attentional response are not fully known. We used the line-motion illusion (Hikosaka et al., 1991) to investigate the optimal cue properties that evoke visual attention. We found that visual attention is driven primarily by the luminance contrast of the cue. Furthermore, by manipulating the spatial, chromatic, and contrast properties of cues, we found that magnocellular (M) stream biased cues always override the response to parvocellular (P) stream biased cues, even when the P stream biased cues are presented first. Our data suggest that cues that preferentially excite the M pathway predominantly capture visual attention.

Color Perception↗
PubMed1996

Disparity tuning of the stereoscopic (cyclopean) motion aftereffect.

Across five experiments this study investigated the disparity tuning of the stereoscopic motion aftereffect (adaptation from moving retinal disparity). Adapting and test stimuli were moving and stationary stereoscopic grating patterns, respectively, created from dynamic random-dot stereograms. Observers adapted to moving stereoscopic grating patterns presented with a given disparity and viewed stationary test patterns presented with the same or differing disparity to examine whether the motion aftereffect is disparity contingent. Across experiments aftereffect duration was greatest when adapting motion and test pattern both were presented with zero disparity and in the plane of fixation. Aftereffect declined as disparity of adapting motion and/or test pattern increased away from fixation, even under conditions in which depth position of adapt and test was equal. This argues against a relative depth separation explanation of the decline, and instead suggests that the amount of adaptable substrate decreases away from fixation.

Adaptation, Physiological↗
PubMed1995

Visual attention mechanisms show a center-surround organization.

The sudden onset of a cue triggers visual attention, which then enhances visual processing in the zone near the cue. This enhancement causes a motion illusion in subsequent stimuli presented near the cue. At greater separations from the cue, the illusory motion reverses direction, indicating prolonged processing speed. Measurements of the strength and direction of illusory motion at increasing separations from the cue reveal an attentional 'perceptive field' with an excitatory center at the locus cued and an inhibitory surround subtending the remaining visual field. These findings help explain the traditional attentional 'benefits' and 'costs' of attention.

Adult↗
PubMed1994

A sensory explanation for visual attention deficits in the elderly.

BACKGROUND: Reduced visual attention has been implicated as a major factor in age-related deficits of real-world functioning such as driving. However, the contribution of sensory factors to visual attention deficits has not been delineated. The magnocellular stream, which is diminished in aging, provides the dominant input to attention, and could provide a direct visual sensory explanation for these attentional losses. METHODS: We measured temporal response curves for transient visual attention in older and younger subjects. Attentional cues stimulated both the magnocellular and parvocellular streams. RESULTS: Older subjects exhibited slower, weaker responses than younger subjects. The time course in younger subjects agreed with that obtained for magnocellular(M)-biased stimuli, whereas that of older subjects agreed with parvocellular(P)-biased responses. CONCLUSIONS: The activation of transient visual attention is slower and weaker for elderly subjects, reflecting a reduced magnocellular input. This marks a primary visual cause for visual attention deficits of the elderly.

Adult↗
PubMed1993

A defective visual pathway in children with reading disability.

BACKGROUND: The possibility that reading disability in children is associated with visual problems is in dispute. We sought to test the existence of this association by using electrophysiologic techniques to measure the processing of visual information in the magnicellular and parvicellular visual pathways of the brain. METHODS: Visual evoked potentials were measured with scalp electrodes in children 8 to 11 years old who were normal readers and in those with reading disability. The potentials were measured for targets with low (0.5 cycle per degree of visual angle) and high (4.5 cycles per degree) spatial frequency, surrounded by either a steady background or a uniform-field flickering 12 times per second. A flickering field normally reduces the amplitude and increases the latency of a transient potential evoked by a low-spatial-frequency target, which preferentially excites the magnicellular visual pathway, but has little effect on the response to a high-spatial-frequency target. RESULTS: With a steady background, the latencies of the early components (N1 and P1) of the visual evoked potentials were longer in the reading-disabled children than in the normal readers when the low-spatial-frequency target was used, but not when the high-spatial-frequency target was used. In normal readers, the flickering background increased the latency and reduced the amplitude of the early components, whereas in the reading-disabled children only the amplitude was affected. No differences were observed in either group with the high-spatial-frequency target. CONCLUSIONS: The pattern of results suggests that the response of the magnicellular visual pathway is slowed in reading-disabled children, who do not, however, have a general slowing of the visual response. The possibility that there is a cause-and-effect relation between these findings and reading disability will require further study.

Child↗
PubMed1992

The perceived duration of gratings.

Since visible persistence of grating patterns increases with spatial frequency, it is often inferred that the perceived duration of a grating is also longer at higher spatial frequencies. However, other work has demonstrated that the perceived onset of a grating is also delayed at higher spatial frequencies. Thus it is impossible to infer the subjective duration from the results of visible persistence studies alone. In order to estimate perceived duration in the present study, reaction times (RTs) to grating onsets and offsets were measured for a range of spatial frequencies. The results indicate that although the perceived duration (ie the difference between offset and onset RTs) was consistently longer than the physical duration, the estimates of perceived duration did not vary with changes in spatial frequency. Differences between the present results and earlier findings are interpreted in the context of the different methods used to measure perceived offset.

Attention↗
PubMed1991

Relationship between response latency and amplitude for ganglion and geniculate X- and Y-cells in the cat.

This study investigates the relationship between visual response latency and amplitude in the retina and dorsal lateral geniculate nucleus (dLGN) of the anesthetized, paralyzed cat. The discharge rate profiles of retinal ganglion and dLGN X- and Y-cells were measured on a trial by trial basis during repeated stimulation with sinusoidal grating patterns. Latencies of response onsets and peaks were regressed linearly against different measures of response amplitude to determine the extent of covariance. In general, response amplitude was a poor predictor of response latency for both retinal ganglion and geniculate cells. The results suggest that response latency, which changes systematically with stimulus spatial frequency and/or contrast, is not a trivial consequence of discharge rate at either level of the visual system.

Animals↗
PubMed1990

Clinical implications of parallel visual pathways.

Visual information travels from the retina to visual cortical areas along at least two parallel pathways. In this paper, anatomical and physiological evidence is presented to demonstrate the existence of, and trace these two pathways throughout the visual systems of the cat, primate, and human. Physiological and behavioral experiments are discussed which establish that these two pathways are differentially sensitive to stimuli that vary in spatial and temporal frequency. One pathway (M-pathway) is more sensitive to coarse visual form that is modulated or moving at fast rates, whereas the other pathway (P-pathway) is more sensitive to spatial detail that is stationary or moving at slow rates. This difference between the M- and P-pathways is related to some spatial and temporal effects observed in humans. Furthermore, evidence is presented that certain diseases selectively comprise the functioning of M- or P-pathways (i.e., glaucoma, Alzheimer's disease, and anisometropic amblyopia), and some of the spatial and temporal deficits observed in these patients are presented within the context of the dysfunction of the M- or P-pathway.

Animals↗
PubMed1990

Electroretinograms and visual evoked potentials in long-term monocularly deprived cats.

The effects of long-term monocular lid-suture deprivation on visual-evoked cortical potentials (VEPs) and flash- and pattern-evoked electroretinograms (FERGs and PERGs, respectively) were assessed in the cat. VEPs were virtually eliminated when recorded with the deprived eye, indicating that the lid suture produced a severe amblyopia in that eye. In contrast, FERGs and PERGs were more similar for both deprived and nondeprived eyes and comparable to those recorded in normal animals. The current findings demonstrate that long-term deprivation (3-4 yr) does not produce systematic changes in the electroretinogram.

Amblyopia↗
PubMed1989

The effects of a luminance-modulated background on the grating-evoked cortical potential in the cat.

Averaged grating-evoked cortical potentials were recorded from area 17 of awake cats. Peak latency of early components of the visual-evoked potential (VEP) response to stimulus onset increased as a function of spatial frequency, while amplitude tended to be largest at intermediate spatial frequencies. Latency increased and amplitude generally decreased to lower spatial-frequency stimuli (less than 0.25 cycle/deg) in the presence of a uniform flickering field (UFF). The UFF had a relatively small or opposite effect on peak latency and amplitude for higher spatial-frequency stimuli (greater than 0.50 cycle/deg). The VEP response to stimulus offset was present only at low spatial frequencies and was virtually eliminated by the presence of the UFF. The effects were similar whether the target and UFF background were simultaneously presented or briefly separated; however, the UFF had no effect when the two were spatially separated. The effects of the UFF background on VEP onset response increased with increasing temporal frequency from 2-8 Hz; offset responses were affected similarly at all temporal frequencies. These effects are similar to those observed in humans and suggest that two spatio-temporally tuned mechanisms contribute to the early VEP response. In the cat, the mechanisms seem to correspond to X and Y cells in the dorsal lateral geniculate nucleus.

Animals↗
PubMed1988

Distribution of opiate receptors within visual structures of the cat brain.

The distributions of mu, delta, and kappa opiate receptors within visual regions in the cat cortex, thalamus and midbrain were determined by in vitro autoradiography. The overall distribution of receptors was examined using [3H]-etorphine, a ligand that nonselectively labels all types of opiate receptors. [3H]-[D-Ala2, N-Me-Phe4,Gly(ol)5]-enkephalin (DAGO) was used to selectively label mu receptors, [3H]-[D-Pen2, 5]-enkephalin (DPDPE) for delta receptors, and [3H]-bremazocine for kappa receptors. Each of the areas examined showed clear opiate receptor binding with [3H]-etorphine and a differential distribution of mu, delta, and kappa receptors. Compared to other cortical regions, opiate binding in layers 3 and 4 of areas 17 and 18 was sparse. In the adjacent areas a more uniform distribution across layers was observed. The density of kappa opiate receptors was greater in cortex than in subcortical structures, whereas the reverse was the case for mu receptors. Nevertheless, all three types of opiate receptors were found in the ventral and dorsal subdivisions of the lateral geniculate (LGN), the pulvinar complex, and the suprageniculate nucleus. In the midbrain, the superficial layers of the superior colliculus were heavily labelled with the mu receptor ligand, and modestly with the kappa ligand. Compared with other midbrain and diencephalic areas, delta binding was low in the superior colliculus. These results suggest that the diverse effects of opiates on visual perception are mediated by the unique distributions of opiate receptor types throughout the visual areas in the brain.

Animals↗
PubMed1988

Response variability of X- and Y-cells in the dorsal lateral geniculate nucleus of the cat.

1. We measured the variability of neural responses in the dorsal lateral geniculate nucleus (dLGN) of the anesthetized, paralyzed cat during repeated visual stimulation with sinusoidal grating patterns. Results are reported for 11 X-cells and 16 Y-cells recorded in laminae A and A1. 2. The responses of most X- and Y-cells varied markedly from trial to trial. The standard deviations of prestimulus, base-line discharge rate. In contrast, the standard deviations of poststimulus responses increased only slightly or not at all with increases in mean discharge rate. 3. Standard deviations of poststimulus responses to optimal stimuli were about one-third the size of mean discharge rates. Relative variability (standard deviation/mean) increased markedly and in nonlinear fashion with decreases in response amplitude, which resulted in considerable overlap of base-line and poststimulus response distributions when stimuli were less than optimal.

Animals↗
PubMed1987

Visual latency of ganglion X- and Y-cells: a comparison with geniculate X- and Y-cells.

Visual response latencies and rise times of X and Y ganglion cells recorded in the optic tract of anaesthetized, paralyzed cats were measured during repeated stimulation with sinusoidal gratings. These measures were compared with visual latencies and rise times of X- and Y-cells in the dorsal lateral geniculate nucleus. Measurements were restricted to individual trials on which the instantaneous discharge rate exceeded a criterion amplitude defined in terms of the statistics of the baseline activity of each cell in order to screen out false alarm responses. The onset and peak latencies of ganglion Y-cells are about 10-15 msec shorter than those of ganglion X-cells at low spatial frequencies (less than 0.25 c/deg) but about 10-20 msec longer at higher spatial frequencies (greater than 0.75 c/deg/). The onset latencies of geniculate X- and Y-cells lag their ganglion counterparts by 10-20 msec. Despite a delay in onsets of geniculate responses, the peak latencies of geniculate and ganglion X-cells are similar, and peak latencies of geniculate Y-cells are even shorter than those of their ganglion inputs. The short latencies of the peak responses of geniculate Y-cells are related to their short response rise times. A functional consequence of the bursty, but fast responses of geniculate Y-cells may be to accelerate the processing of lower spatial frequencies by the retino-geniculate Y-cell pathway.

Action Potentials↗
PubMed1986

Spatial displacement sensitivity of X- and Y-cells in the dorsal lateral geniculate nucleus of the cat.

The sensitivity of X- and Y-cells in the dorsal lateral geniculate nucleus of the cat to small, temporally modulated displacements of grating stimuli was measured at 0.175, 0.25, 0.50, 1.00, and 2.00 c/deg. For every cell, two threshold measures were determined: first, a contrast threshold with a counterphase grating and then a displacement threshold with a grating matched in spatial frequency, but whose contrast was 2.5 times the threshold value. The results showed that displacement thresholds of both X- and Y-cells decreased with increasing spatial frequency. At low spatial frequencies, mean displacement thresholds of X- and Y-cells were similar, but at intermediate spatial frequencies, Y-cell thresholds were lower than X. X-cell displacement thresholds were lower than Y only at the highest spatial frequency tested. Consistent with previous reports, contrast thresholds also varied with spatial frequency for both X- and Y-cells. The local luminance differences produced by the contrast threshold and displacement threshold stimuli for the two classes of cells were compared. Across all spatial frequencies, the change in position of the gratings at displacement threshold produced smaller luminance differences than the counterphase gratings at contrast threshold. This enhanced sensitivity of X- and Y-cells to a local luminance changes produced by grating displacement was related to the high spatial contrast of the grating and not to the displacement per se.

Action Potentials↗
PubMed1986

Visual response latency of X- and Y-cells in the dorsal lateral geniculate nucleus of the cat.

Visual response latencies and rise times of X- and Y-cells in the dorsal lateral geniculate nucleus (dLGN) of anaesthetized, paralyzed cats were measured during repeated stimulation with sinusoidal grating patterns. Measurements were restricted to individual stimulus trials on which the instantaneous discharge rate exceeded a criterion amplitude defined in terms of the baseline activity of each cell. The latencies of response onsets and response peaks were systematically related to the spatial frequency and contrast of the grating stimuli. Response latencies of Y-cells were shortest for gratings of low spatial frequency (0.17 c/deg) and increased monotonically with increases in spatial frequency. Response latencies of X-cells were shortest for gratings of intermediate spatial frequency (0.75 c/deg) and longer for lower and higher spatial frequencies. Latencies decreased monotonically with increases in stimulus contrast from 5 to 40% for both X- and Y-cells. In general, short-latency responses were less variable than long-latency responses. This was true for absolute as well as relative measures of variability. The mean onset and peak latencies of Y-cell responses were 10-15 msec shorter than the corresponding latencies of X-cell responses to stimuli of optimal spatial frequency and contrast. The rise times (latency of response peak minus latency of response onset) of Y-cell responses were consistently shorter than those of X-cells in spite of the higher peak responses of Y-cells. The results of this study are consistent with the idea that low spatial frequency information is passed through the lateral geniculate nucleus more quickly than is high spatial frequency information. These data provide support for models of visual processing wherein a coarse, global analysis of the visual scene by Y-cells precedes a finer, local analysis by X-cells.

Action Potentials↗
PubMed1986

The effects of monocular deprivation on the visual latency of geniculate X- and Y-cells in the cat.

Monocular lid suture deprivation during early visual development of the cat alters the temporal flow of retinal information as it passes through the dorsal lateral geniculate nucleus. The latencies of Y-cells located in the deprived layers and of both X- and Y-cells in the non-deprived layers are shorter than the latencies of their counterparts in normally reared cats. The visual response onset latencies of X-cells located in the deprived geniculate layers lag those of X-cells in the non-deprived layers.

Animals↗