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PubMed1996

Serial position effects in visual short-term memory for words and abstract spatial patterns.

Two experiments tested the effects of list position, and retention-interval in recognition for two distinct stimulus categories in young adults. Stimulus categories were spatial abstract patterns and words presented on a computer screen. At short delay intervals recency effects predominates and at longer delay intervals a primacy effect predominates in both experiments, indicating similar basic memory processes producing the serial position functions for the two different categories of visual stimuli, but as length of retention-interval increases, memory for first list items improves for words and remains constant for abstract patterns. Recency functions are similar for both stimulus categories tested.

Adult↗
PubMed1987

A developmental approach to reading disability: accuracy and speed criteria of normal and deficient reading skill.

The constructs of accuracy and speed were adopted as performance criteria against which to define 2 clinical samples of disabled readers. Accuracy-disabled subjects had failed to achieve reliable age-appropriate word recognition skills. Rate-disabled readers were age-appropriate in word recognition accuracy but deficient in reading speed. These disabled readers were compared to fluent normal children selected to be reading at the same level of accuracy as the rate-disabled subjects but at a significantly faster rate. All aspects of the accuracy-disabled subjects' reading systems proved deficient, and these children were less able to learn new sound-symbol associations in a task simulating initial reading acquisition. The rate-disabled subjects exhibited a basic deficit in word recognition speed, compromised accuracy when reading in context, and compromised spelling when competing visual patterns were available. A multidimensional oral language impairment was found to accompany the accuracy disability, while the rate disability appeared restricted to language in its visible form and the naming of visual representations. A visual naming speed impairment was associated with both profiles of deficient reading skill.

Adolescent↗
PubMed2002

Event-related brain potential evidence for a response of inferior temporal cortex to familiar face repetitions.

We investigated immediate repetition effects in the recognition of famous faces by recording event-related brain potentials (ERPs) and reaction times (RTs). Participants recognized celebrities' faces that were preceded by either the same picture, a different picture of the same celebrity, or a different famous face. Face repetition caused two distinct ERP modulations. Repetitions elicited a strong modulation of an N250 component ( approximately 200-300 ms) over inferior temporal regions. The N250 modulation showed a degree of image specificity in that it was still significant for repetitions across different pictures, though reduced in amplitude. ERPs to repeated faces were also more positive than those to unprimed faces at parietal sites from 400 to 600 ms, but these later effects were largely independent of whether the same or a different image of the celebrity had served as prime. Finally, no influence of repetition was observed for the N170 component. Dipole source modelling suggested that the N250 repetition effect (N250r) may originate from the fusiform gyrus. In contrast, source localisation of the N170 implicated a significantly more posterior location, corresponding to a lateral occipitotemporal source outside the fusiform gyrus.

Adolescent↗
PubMed1994

Pattern reversal visual evoked potentials following early treatment of unilateral, congenital cataract.

OBJECTIVE: To describe the pattern reversal visual evoked potentials (VEPs) that were used to monitor and quantify early visual development following treatment for dense, unilateral, congenital cataract. DESIGN: Longitudinal prospective study. PATIENTS: Six infants who underwent surgery and contact lens correction before age 5 months and who had good compliance with occlusion therapy throughout the first 3 years of life. RESULTS: Initially, VEPs from aphakic eyes showed marked abnormalities, including small amplitudes, prolonged latencies, missing components, and absent VEPs to small check sizes. Threshold check size was elevated by 3 octaves or more. With part-time occlusion of the opposite eye, VEPs normalized rapidly in the first year, but residual deficits remained to age 4 years when visual acuities were between 20/50 and 20/120 in aphakic eyes. Threshold check size clearly differentiated between aphakic and normal eyes and was the only VEP parameter that was correlated with single-letter visual acuity. Thus, threshold check size had greater clinical use than measures of pattern VEPs based on latency, amplitude, or waveform. CONCLUSIONS: Patients treated for unilateral congenital cataract, who have early surgery and contact lens correction and comply with occlusion therapy, show a period of rapid VEP maturation and have a good visual prognosis.

Aphakia, Postcataract↗
PubMed1989

Presence of ghost doublets of coded neuronal patterns: relation to synaptic memory storage.

Recent evidence demonstrates that controlled visual stimuli cause the generation, in the primary visual cortex of rhesus monkey cells, of large numbers of very precisely replicating copies of complex patterns of discharge consisting of three or more spikes, the patterns of which presumedly code for specific qualities of the stimuli presented. We present evidence that the copies of precisely replicating triplets of spikes, generally not exceeding 100 ms in duration, occur in close time proximity to many copies of highly precise "ghost" doublets. These doublets are defined as patterns consisting of two pulses, with precise separations in time, specifically those that would be generated if any one of the pulses making up a given replicating triplet were missing. In striking contrast, nonreplicating triplets (also present in these records)--that is, triplets made up of intervals that are not present in replicating triplets--are not accompanied by such ghost doublets. The persistence (memory) of capacity to produce such ghost doublets decays according to two independent kinetic rules. The first of these results in the disappearance of such doublets within about 0.1 s as measured by two independent methods, whereas the second disappears only after several minutes or longer. These results provide strong evidence consistent with the notion that at least some parts of the brain transmit, store representations of, and retrieve qualitative information through the use of a code consisting of specific patterns of nerve discharges in time.

Animals↗
PubMed1994

Event-related brain potentials reflect semantic priming in an object decision task.

Subjects made speeded object decisions about target line drawings which were preceded by semantically related or unrelated prime line drawings. One hundred of the targets depicted real objects and 50 others were unrecognizable non-objects. Similar to a recent picture-matching study, the ERPs from this study generated a larger negativity for unrelated than for related target pictures, between 325 and 550 msec (N400). Although these differences had a similar time course to those seen for the N400 component in semantic priming lexical decision tasks, they were more frontally distributed and were larger over the left rather than the right hemisphere. Non-objects, which were the picture equivalent of pseudowords, produced an even larger negativity with a somewhat different distribution. The results are discussed with regards to recent claims about amodal conceptual memory processes.

Adult↗
PubMed1988

Pattern visual evoked cortical potential waveforms and spatial frequency characteristics in children.

Development of visual evoked cortical potential waveforms and the spatial frequency characteristics of the pattern reversal stimuli were studied in children from 7 weeks to 15 years of age. All subjects were born at term. Waveforms were found to change rapidly during the first several months after the birth, from single slow positive peaks to negative-positive-negative complex. Spatial frequency characteristics in N2 latencies were observed to develop rather slowly up to school age. Long-term development of pattern vision in children was suggested.

Adolescent↗
PubMed1989

Abnormality of the pattern electroretinogram and pattern visual evoked cortical response in esotropic cats.

In six 3-week-old kittens, the tendon of the lateral rectus muscle of one eye was sectioned under anaesthesia in order to induce an esotropic (nasally-directed) squint. At maturity, the pattern electroretinogram (PERG) and pattern visual evoked response (PVER) were recorded under anaesthesia to phase-reversal at 1.67 Hz of a 0.5c/deg square wave grating pattern of 75% contrast. Refraction was determined by retinoscopy and confirmed by recording the PERG for different trial lenses. The amplitude and time-to-peak of the PERG and PVER were compared between operated and unoperated eyes, and with the responses of one normal and two sham-operated cats. With stimulation of the operated eye, the amplitude of the PVER was consistently reduced by 50% compared with the non-operated eye, confirming that the cats had become amblyopic as a result of the squint. While the appreciable inter-eye variations in the amplitude of the PERG of the normal and sham-operated cats precluded identification of a change in the esotropic cats, there was a consistent prolongation of the time-to-peak of the PERG by 50% with stimulation of the operated eye. This result is consistent with a retinal component to strabismic amblyopia.

Amblyopia↗
PubMed1990

Spatio-temporal interactions and the spatial phase preferences of visual neurons.

We recorded single neuron responses in the cat's lateral geniculate nucleus (LGN) and visual cortex to compound stimuli composed of two sinusoidal gratings in a 2:1 frequency ratio. To probe visual receptive field symmetry, we varied the relative spatial phase of the two components and measured the effect on neuronal responses. We expected that on-center LGN neurons would respond best to gratings combined in positive cosine (bright bar) phase, while off-center LGN neurons would respond best to gratings combined in negative cosine (dark bar) phase. When drifting stimuli were used, cells' phase preferences were roughly 90 deg away from the expected values; when stationary, contrast-modulated stimuli were used, phase preferences were as originally predicted. Computer simulations showed that this discrepancy could be explained by taking into account the cells' temporal properties. Thus, tests using drifting stimuli confound the spatial structure of visual neural receptive fields with their temporal response characteristics. A small sample of data from cortical neurons reveals the same confound.

Action Potentials↗
PubMed1990

The effects of contrast on the linearity of spatial summation of simple cells in the cat's striate cortex.

Non-linearities of spatial summation were examined in simple cells in the cat's striate cortex. The degree of non-linearity was assessed from an examination of the waveforms of the responses to moving sinusoidal gratings and was quantified by a measure called relative modulation. Relative modulation was affected little by changes in contrast at either optimal or non-optimal spatial frequencies. The non-linearities of spatial summation exhibited by some simple cells are, therefore, essential. Those simple cells which exhibit linear spatial summation are no less linear at high stimulus contrasts. These results support a 'push-pull' model of simple cell receptive field organization in which ON and OFF centre l.g.n. input is combined both additively and subtractively.

Animals↗
PubMed1982

Organization of neurones preferring similar spatial frequencies in cat striate cortex.

The optimal spatial frequencies were determined for over 300 neurones in cat striate cortex. Neurones recorded within about 100 microns were more likely to have similar optimal spatial frequencies than were neurones recorded at greater separations. But, even neurones recorded close together sometimes differed markedly in their optima; these differences could not be attributed to differences in receptive field eccentricity. When one lamina was sampled more than once, on different electrode penetrations, the different samples of neurones did not often have similar optimal spatial frequencies. To investigate whether neurones in laminae or in columns prefer the same spatial frequencies, data from normal and oblique penetrations were compared. Little difference in the degree of organization was seen in the two kinds of penetrations.

Animals↗
PubMed1982

Orientation deprivation in cat: what produces the abnormal cells?

When an animal is reared with goggles containing stripes of a single orientation, many cells in the visual cortex become abnormal. To find out whether these abnormal cells result from orientation deprivation per se or from other features of goggle rearing we reared kittens with goggles containing stripes of many orientations. The data suggest that orientation deprivation contributes to the development of abnormal cells but is not its sole cause.

Animals↗
PubMed1982

On the sensitivity of complex cells in feline striate cortex to relative motion.

Responses of superficial-layer, texture-sensitive complex cells in cat striate cortex to relative motion between an oriented bar stimulus and its textured background were recorded. Some cells responded best to motion in one particular direction across the receptive field of the cell, irrespective of whether the bar and background moved simultaneously in the same (in-phase) or opposite (antiphase) directions. Others showed a clear preference for either in-phase or antiphase relative motion, irrespective of direction of motion across the receptive field.

Animals↗
PubMed1988

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.

Animals↗
PubMed1988

State dependent activity in monkey visual cortex. II. Retinal and extraretinal factors in V4.

Responses were recorded from isolated neurons in the visual cortex of rhesus monkeys while they performed an orientation match to sample task. In each trial the animal was first cued with randomly selected orientation, and then presented with a sequence of gratings whose orientations were randomly selected. The animal was required to release a switch when it saw a grating that matched the cued orientation. For some recordings the animal was given a tactile cue by having it feel the orientation of a grooved plate that it could not see. In other experiments the cue orientation was presented visually on the screen in front of the animal and then removed before the sequence of gratings was presented. Using this task it was possible to determine if a neuron's response to a particular orientation was affected by whether or not it was the orientation for which the animal was looking. Over half the neurons examined in V4 (110/192) responded differently to the visual stimuli when the animal was cued to look for different orientations. For some neurons responses to all stimuli were strong when the animal was cued to look for a particular orientation, but weak when the same stimuli were presented in trials where the animal had been cued to look for another orientation. This type of sensitivity was found in neurons recorded while the animal was given a tactile cue, and also in other neurons tested when a visual cue was used, suggesting that the activity was not of direct sensory origin. In support of this, neurons in V4 were not strongly affected when the animal felt the grooved plate while not performing the orientation matching task. The prevalence of behavioral effects that was found using the orientation matching task suggests that extraretinal signals represent a prominent component of the activity in V4 of the behaving monkey.

Animals↗
PubMed1994

Influence of simultaneous pattern-reversal electroretinogram recording on visual evoked potentials.

Little is known about the influence of the presence of a gold-foil electrode on pattern-reversal visual evoked potential recording, although simultaneous pattern-reversal electroretinography has been applied in several clinical investigations. We compared the results of pattern-reversal visual evoked potentials simultaneously recorded with pattern-reversal electroretinograms with those obtained during separate pattern-reversal visual evoked potential recording in 10 normal subjects. Transient response (reversal rate, 1 Hz; check size, 30') and steady-state response (reversal rate, 5 Hz; check size, 120', 60', 30', 15' and 7.5') were analyzed under the stimulus contrast condition of 90%. Neither P100 latency in transient responses nor amplitudes in steady-state responses exhibited significant change at any check size when they were recorded separately or simultaneously with pattern-reversal electroretinograms. The results suggest that the gold-foil electrode exerts no significant influence on pattern-reversal visual evoked potentials. Simultaneous pattern-reversal electroretinogram and visual evoked potential recording is therefore confirmed to be a clinically useful method. This procedure makes the synchronous recording of both responses possible under the identical stimulus conditions.

Adult↗
PubMed1993

Pattern visual evoked potentials in cases of ambiguous acuity loss.

Thirty patients were referred to our visual evoked potential laboratory with complaints of profound acuity loss in one or both eyes. However, the objective ophthalmologic findings were normal, including pupillary reaction, and anterior segment and fundus examinations. Transient visual evoked potentials to a 2.3-c/deg sinusoidal grating pattern were found to be present in 26 of these 30 patients. Visual evoked potentials may be used as a measure of afferent pathway integrity.

Adolescent↗