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PubMed2006

Resonant neurons and bushcricket behaviour.

The resonant properties of the intrinsic dynamics of single neurons could play a direct role in behaviour. One plausible role is in the recognition of temporal patterns, such as that seen in the auditory communication systems of Orthoptera. Recent behavioural data from bushcrickets suggests that this behaviour has interesting resonance properties, but the underlying mechanism is unknown. Here we show that a very simple and general model for neural resonance could directly account for the different behavioural responses of bushcrickets to different song patterns.

Acoustic Stimulation↗
PubMed2006

Spinocerebellar ataxia type 2 olfactory impairment shows a pattern similar to other major neurodegenerative diseases.

Olfactory function is affected in different neurodegenerative diseases. Recently, it has been found that some hereditary ataxias are also associated with significant olfactory impairment. However, the initial findings did not examine the nature of the olfactory impairment associated with these ataxias. In the present article the effect of spinocerebellar ataxia type 2 (SCA2) on olfactory function was studied in 53 SCA2 patients and 53 healthy control subjects from Holguín, Cuba. Several tests were applied to evaluate olfactory threshold, description, identification and discrimination. The results show significant impairment in SCA2 patients on all olfactory measurements, and the pattern of olfactory deficits found suggests that they have much in common with those reported for other neurodegenerative diseases such as Parkinson's and Alzheimer's diseases.

Adult↗
PubMed2005

Self-organization in the olfactory system: one shot odor recognition in insects.

We show in a model of spiking neurons that synaptic plasticity in the mushroom bodies in combination with the general fan-in, fan-out properties of the early processing layers of the olfactory system might be sufficient to account for its efficient recognition of odors. For a large variety of initial conditions the model system consistently finds a working solution without any fine-tuning, and is, therefore, inherently robust. We demonstrate that gain control through the known feedforward inhibition of lateral horn interneurons increases the capacity of the system but is not essential for its general function. We also predict an upper limit for the number of odor classes Drosophila can discriminate based on the number and connectivity of its olfactory neurons.

Animals↗
PubMed2004

Effect of room illuminance on monitor black level luminance and monitor calibration.

In this article we demonstrate the effect of room illuminance and surrounding monitor black level luminance on image quality for soft copy interpretation. Luminance values of a 10% central target and image quality evaluations and observer performance using a contrast-detail mammography (CDMAM) phantom demonstrate these effects. Our results indicate that high room illuminance has a more damaging effect on image quality when the surrounding monitor luminance is 0% to 5% of the maximum monitor luminance. The effect of room illuminance is less obvious when the surrounding monitor luminance is 20% of the maximum.

Calibration↗
PubMed1984

The efficiency of the central and peripheral retina in driving human optokinetic nystagmus.

Previous experiments to decide whether the gain of optokinetic nystagmus (OKN) is increased or decreased by occlusion of the central retina involved the use of stationary edges on the occluder and unmatched contrasts. With these factors controlled, it was confirmed that OKN gain is severely reduced by occlusion of the central retina but only at stimulus velocities above about 30 degrees/sec. The gain of horizontal OKN was found not to increase with increasing width of the display if the lateral edges are blurred. The high gain of centrally driven OKN may be related to the ability of higher mammals to stabilize the images of objects at a given distance in a complex parallactic visual field.

Humans↗
PubMed1985

The influence of nystagmoid oscillation on contrast sensitivity in normal observers.

Normal observers subjected to retinal image motion equivalent to that experienced by congenital nystagmats were found to display a contrast sensitivity function with characteristics similar to those shown by nystagmat observers. The amplitude, frequency and waveform (and hence foveation time) of nystagmic oscillation were varied, with alteration of the waveform producing the most significant effect on the contrast sensitivity function. The pseudocycloid waveform with the longest percentage foveation time per cycle was commensurate with the best visual resolution of medium-to-high spatial frequency targets. For all waveforms the length of the foveation period showed good correlation with visual resolution of the targets.

Adult↗
PubMed1985

Asymmetries of optokinetic nystagmus in amblyopia: the effect of selected retinal stimulation.

Open loop optokinetic eye movements were measured in response to monocular nasalward and temporalward visual field movement presented at four selected retinal sites in 6 strabismic amblyopes and 4 normal observers. Stimulus sites included the central retina (10 X 10 deg), a large field (40 X 32 deg), a large peripheral field with the center (10 X 10 deg) blocked out and a hemiretinal field (15 X 32 deg) excluding the fovea. We found directional preferences of OKN in amblyopia to nasalward stimulus movement for the foveal and concentric peripheral stimuli. The results of peripheral hemiretinal optokinetic stimulation of amblyopic subjects revealed a deficient OKN slow phase response from the temporal hemiretina, particularly for temporalward stimulus movement. There was no marked asymmetry of OKN in the normal group for the concentric stimuli. A normal preference was found for nasalward and temporalward stimulus field movement imaged on the nasal and temporal hemiretinae respectively. These results are interpreted in terms of a model of cortical and subcortical pathways for OKN derived from comparative studies of cat and monkey.

Adult↗
PubMed1986

Optokinetic nystagmus: the effects of stationary edges, alone and in combination with central occlusion.

In Experiment 1 we investigated the independent and combined effects of horizontal OKN of stationary edges and occlusion of the central retina. For a display 60 degrees wide moving at 30 degrees/sec a symmetrically placed pair of vertical nonoccluding bars suppressed OKN when near the center of the display but had no effect when 30 degrees apart. A 7 degrees-high 60 degrees-wide central occluder reduced OKN gain by 37%. However, a central occluder with edges only 30 degrees wide abolished OKN. In Experiment 2 this interaction between central occlusion and stationary edges was confirmed with a wider display over a range of stimulus velocities and configurations. A functional explanation of this interaction is presented.

Adult↗
PubMed1986

Human smooth pursuit: effects of stimulus extent and of spatial and temporal constraints of the pursuit trajectory.

We compared the quality of monocular smooth pursuit obtained with either a single point, a full-field stripe pattern or their combination as the target for unidirectional stimulus motion at velocities between 9 and 90 deg/sec. A point target moving in a fixed trajectory maximally constrains target selection as well as pursuit trajectory, whereas a full-field multicontoured pattern leaves the subject maximal freedom in these respects. To unconfound effects of pattern extent from those of spatial and temporal constraints, we presented point targets under conditions in which the subject was free to choose the location, extent and temporal structure of his pursuit trajectory ("free range"). Pursuit velocity gains were lowest for the point target moving in a fixed trajectory. Gain improved when the subject was free to pursue the same target moving at the same velocity in his own preferred range and rhythm. A further improvement was reached by showing the stripe pattern in addition to, and moving in conjunction with the spot. A final increase in gain occurred when the spot was removed, and the subject was allowed to pursue any feature of the uniformly moving, multicontoured pattern. No asymmetries were found between monocular pursuit with the right or the left eye, pursuit of rightward and leftward motion or between nasal- and temporalward motion. Effects of the type of target on the structure of the nystagmoid pursuit eye movements were slight or absent.

Eye Movements↗
PubMed1986

Non-conjugate monocular optokinetic nystagmus in cats.

Binocular eye movement during horizontal monocular optokinetic nystagmus was studied in cats. When the stimulus pattern was moved slowly (at 1-10 deg/sec in temporonasal direction and 1 deg/sec in nasotemporal, averages of four cats), the gain (slow phase velocity/stimulus velocity) of the covered eye was significantly lower than that of the seeing eye. At the faster stimulus velocities, these differences of gain decreased.

Animals↗
PubMed1987

Stereoscopic contours and optokinetic nystagmus in normal and stereoblind subjects.

Moving stereoscopic contours in a dynamic random-dot stereogram have been previously shown to induce optokinetic nystagmus in subjects with normal stereopsis. For this to be validated as an objective test of stereopsis, stereoblind subjects must also be shown not to develop OKN, especially since it has been shown that the optomotor system of stereoblind individuals retains sensitivity to some cyclopean stimuli. In this report we verify that stereoblind subjects do not have an optomotor response to stereoscopic contours--regardless of the alignment angle at which the stereo image pair is presented.

Depth Perception↗
PubMed1990

Motion coherence in infants.

Two perpendicular square-wave gratings (i.e. plaids) were used to investigate motion coherence in 1-, 2- and 3-month-old infants. The direction of motion of the stimulus was judged by an adult observer, on the basis of the induced optokinetic nystagmus (OKN) in an eight-alternative eye movement voting paradigm. Infants as young as 1 month of age demonstrated OKN in the direction consistent with motion coherence. There was no significant difference among the performances of 1-, 2- or 3-month-old infants. However, the percentage of trials on which infants demonstrated OKN in the coherence direction was less than that obtained from adults tested with the same paradigm. Movshon, Adelson, Gizzi and Newsome (1985) have suggested that the cohered motion of a complex pattern may be processed after the orientation of the components of the pattern, perhaps in the middle temporal area of the visual cortex (MT). The present results suggest that either young infants and adults process the motion of complex patterns similarly or that the OKN consistent with the direction of motion coherence observed in infants involves subcortical nonoriented visual centers rather than the higher level process which is presumed to occur in adults.

Adult↗
PubMed1990

Binocular motion rivalry in macaque monkeys: eye dominance and tracking eye movements.

When the two eyes are exposed to markedly different patterns, perception becomes unstable, falling into oscillations, so that the image of one eye is seen first and then that from the other. With large stimuli the alternation is piecemeal, whilst when small stimuli are used the whole pattern alternates in unison. The purpose of this study was to determine whether a reliable, objective indicator of the perceptual state during binocular rivalry could be developed in the nonhuman primate. Monkeys (Macaca mulatta) were trained to discriminate direction of motion when presented with vertically drifting gratings moving in opposite directions in the two eyes. A high correlation was found between the direction of the slow phase of the optokinetic nystagmus (OKN) elicited by the drifting gratings during rivalry and the direction of motion reported by the monkey even though the gain of the OKN was reduced during rivalry, and the latency was longer. Behavioral eye dominance during rivalry varied significantly over time, between individuals and as a function of interocular contrast differences. Since the direction of tracking eye movements can be used to reliably monitor perceptual state during binocular motion rivalry, the opportunity exists in nonhuman primates to study the neurophysiological mechanisms underlying motion perception during the perceptually ambiguous condition of binocular rivalry.

Animals↗
PubMed1991

Contrast sensitivity of optokinetic nystagmus.

To determine the threshold characteristics of optokinetic nystagmus (OKN), contrast thresholds for involuntary OKN were measured for gratings of different spatial frequency to yield an OKN-contrast sensitivity function (OKN-CSF). The OKN-CSF resembled an inverted U-shaped function with temporal-to-nasal and nasal-to-temporal movement yielding similar functions. In addition, when psychophysical CSFs were determined for separate form and movement thresholds, it was discovered that the OKN-CSF approximated the psychophysical-movement CSF rather than the psychophysical-form CSF.

Adult↗
PubMed1991

The relationship of luminous intensity and velocity for motion perception and maximum OKN elicitation.

The psychophysiological aspects of the luminous intensity stimulus velocity relationship for perceiving a grating pattern and eliciting optokinetic nystagmus (OKN) with maximum slow-phase velocity were studied in two normal human eyes. The results show that (1) both the luminous intensity and target velocity (within the region from 16-56 deg/sec) have a linear relation to the perception of a grating pattern and eliciting of the maximum OKN. (2) The trends of the relation between perception and elicitation are similar, but the slopes of the regression lines are different. (3) No statistically valid directional effect is found on either visual perception or maximum OKN elicitation in humans who have normal binocular vision. (4) For a given stimulus velocity, OKN gain (slow-phase velocity/stimulus velocity) increases to a saturation point as the stimulus intensity increases. The maximum OKN gain decreases as the stimulus velocity increases.

Humans↗
PubMed1996

Visually elicited head rotation in pigeons (Columba livia).

Horizontal rotational head movements were video-taped from pigeons standing freely in a rotating cylinder. The cylinder carried vertically striped patterns approximating a sinusoidally modulated horizontal intensity distribution. We altered systematically various stimulus parameters: spatial wavelength and contrast of the pattern, angular velocity of the pattern motion and mode of motion onset. We found: (1) both gradual acceleration of the patterned cylinder as well as immediate onset of pattern motion elicit the sequence of smooth following and saccadic resetting movement typical of the rotational "stare" head nystagmus; (2) in experiments with rapid onset of pattern motion, velocity of the smooth following response gradually increases to its steady-state level over a period of about 10 sec; (3) the saccadic head rotations are not stereotyped: larger and shorter saccades follow in an irregular sequence, saccadic velocity and average size varies with stimulus conditions; (4) in the range of 0.9-95 deg/sec, the velocity of the following phase increases in parallel with stimulus speed; (5) in the range of spatial wavelengths of the striped patterns from 6 to 45 deg, at a given drum velocity, patterns of short wavelengths elicit optokinetic head rotations with higher gain (head velocity/drum velocity) than patterns of long wavelengths; (6) response velocity increases with pattern contrast (Michaelson contrast 5, 32 and 75%), following approximately a logarithmic relation; (7) our results on rotational optokinetic head movements support the notion that the neural mechanism underlying motion detection operates like a correlation mechanism.

Animals↗
PubMed1994

Task decision difficulty: effects on ERPs in a same-different letter classification task.

A "same-different" letter pair choice reaction time task was used to compare reaction time, performance accuracy, and P3 amplitude and latency at three levels of task difficulty. Stimulus set was held constant across tasks, and task difficulty was manipulated by instructions to the subject. Subjects delivered a button-press response to designate whether members of each letter pair matched or mismatched on the basis of their physical identity (low difficulty), name identity (medium difficulty), or category identity (vowels/consonants, high difficulty). Task decision difficulty was confirmed by slower reaction times and reduced response accuracy. P3 amplitude was inversely related to task decision difficulty; relatively larger P3s were associated with matched (vs. mismatched) letter pairs. These findings evidence direct effects of task difficulty on P3 amplitude, possibly as the result of "equivocation" related to more difficult task judgments.

Adult↗