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Biomedical subjects

G C Gilmore

Publications and source records attributed to G C Gilmore.

At least 19 recordsLinked to original sources
PubMed1997

The relationship between smooth pursuit performance, motion perception and sustained visual attention in patients with schizophrenia and normal controls.

BACKGROUND: In this study, we tested the hypothesis that low smooth pursuit gain in schizophrenia is related to an abnormality in motion perception. METHODS: The subjects were 19 schizophrenics treated with clozapine and 19 controls. In addition to smooth pursuit and motion perception paradigms, sustained attention was also assessed using a continuous performance task (CPT). RESULTS: In the patient group, there was a statistically significant negative correlation between smooth pursuit gain and motion perception threshold (r = -0.60, P < 0.01). This relationship was not secondary to attention deficits as assessed by the CPT. CONCLUSIONS: Our results are consistent with the notion that the smooth pursuit gain deficit is related to a deficit in motion perception rather than in attention. Brain area V5 (also referred to as "MT' in macaque), located in the parieto-occipital region, is known to be critically important both for motion perception and gain. Thus, our results point to an abnormality in this area in schizophrenia.

Adult↗
PubMed1996

Hallucinations.

Explore the source record for details and available documents.

Aged↗
PubMed1995

Contrast sensitivity in Alzheimer's disease: a 1-year longitudinal analysis.

Spatial contrast sensitivity was evaluated in normal elderly adults and a group with probable Alzheimer's disease (AD) in three sessions over a 1-year period. There was evidence of a reduction over 1 year in contrast sensitivity for static, high spatial frequencies in both groups of subjects. A striking difference between the subject groups was observed in their response to flickered stimuli. Although normal elderly adults yielded good stability in sensitivity for both static and flickered spatial frequencies over the 1 year, AD patients experienced a significant decline in response to flickered (7.5 Hz) stimuli. The significant decline in sensitivity for low contrast, high temporal events in AD patients is consistent with reports of cell loss at the retinal and cortical levels of the magnocellular (M) channel in AD. Thus, the spatial contrast sensitivity change in AD may reflect a more rapid loss of cells specifically in the M channel over a 1-year period.

Adult↗
PubMed1994

Motion perception and Alzheimer's disease.

The motion sensitivity of 15 probable Alzheimer disease (AD) patients and 15 healthy elderly adults was investigated with a correlated motion paradigm. The AD patients exhibited significantly higher thresholds for detecting the direction of motion. Contrast sensitivity for a 2 cpd, 7.5 Hz counterphased stimulus was related to motion threshold in the AD group. There also was a significant relationship between an index of dementia severity, Mini-Mental State Exam (MMSE), and motion sensitivity. The results support the hypothesis proposed from neuroanatomical evidence by Hof and Morrison (1990) that AD results in a disruption of the visual signals mediated by area 17. Further, the data suggest that this disruption of visual processing is linked to the progression of dementia. The study offers support for the hypothesis that AD leads to a deficit in the magnocellular or M pathway of visual processing.

Aged↗
PubMed1994

Perceptual comparison of pulsed and continuous fluoroscopy.

Pulsed fluoroscopy (hereafter called pulsed) at reduced acquisition rates, typically 15 acq/s (pulsed-15), is proposed to reduce x-ray dose in interventional procedures. However, since the human visual system (HVS) acts as a temporal low-pass filter that interacts with such acquisitions, the proper dose for pulsed must be obtained in perception experiments. We determine the dose for low-frame-rate pulsed that gives visualization equivalent to that of conventional 30 acq/s fluoroscopy, hereafter called continuous. Computer-generated phantoms are used. They consist of stationary, low-contrast disks on a flat background containing Poisson noise that mimics quantum noise in fluoroscopy. Image sequences are displayed on the video tachistoscope, a device with considerable display flexibility. Three experimental paradigms are used. (1) In a paired-comparison study, pulsed and continuous are displayed side-by-side on the same monitor, and the visibility of a contrast detail phantom is compared. (2) Using this same display, subjects record the minimally detectable disk contrast (the min-contrast measurement). (3) In a four-alternative forced-choice experiment, a disk is placed in one of four positions, and the subject determines the position of the disk. The methods are complementary--the forced-choice experiment properly eliminates the subjectivity of the observer threshold while the paired-comparison study is much more time efficient. With regard to pulsed and continuous comparisons, remarkable similarity is found between the supra-threshold experiments (1 and 2) and the detectability experiment (3); i.e., the average absolute differences in the equivalent-perception dose as determined by the three measures is approximately 3%. No difference is found between interlaced and noninterlaced display. A relatively small dependence of dose savings on disk size is found with larger disks giving increased dose savings. Average dose savings of 22%, 38%, and 49% are found for pulsed-15, pulsed-10, and pulsed-7.5, respectively.

Fluoroscopy↗
PubMed1992

Visual information decoding deficits in schizophrenia.

Schizophrenic and control subjects were tested on two-flash fusion (TFF) and visual backward masking (VBM) tasks in a repeated measures design. Each subject was tested in a single session. Both tasks used the same equipment and stimuli. There was no difference between the groups in their ability to detect the presence of two separate stimuli in the TFF task. Schizophrenic subjects did require longer interstimulus intervals (ISI) than control subjects to accurately report one of the two targets in the VBM task. Analysis of individual targets reveals that the VBM deficit is a function of the similarity of the target and mask. The more feature detail discrimination necessary, the longer an ISI is required in VBM. The data are interpreted as supporting the conclusion that since the groups did not differ in their performance of the TFF task, which would also have been affected by a sensory abnormality, the deficit in VBM must be explained by reference to a higher level of information processing. The VBM deficit is a failure to decode the target stimulus, and is not simply a function of abnormalities due to an overactive transient channel system.

Adult↗
PubMed1992

Motion perception and aging.

The authors used a correlated motion paradigm to investigate the effects of aging and gender on motion sensitivity. In 2 experiments with a total of 50 elderly and 50 young subjects, motion thresholds were significantly higher for elderly women. The correlated motion signal, which was embedded in random motion, may have been coherent to subjects in much the same way a form is in Witkin's Embedded Figures Test (EFT). In Experiment 2, EFT scores were obtained. A significant positive relationship between motion thresholds and EFT performance was found within each age group. Although gender-related perceptual style differences may contribute to motion perception effects, the authors argue that a common neural factor contributes to performance on both the EFT and the correlated motion task.

Adult↗
PubMed1991

Comparison of two methods of contrast sensitivity assessment with young and elderly adults.

The sensitivity of the neural channels which process spatial frequency information may be assessed by determining the threshold contrast for a range of spatial frequencies. The stability and reliability of two methods of assessment, von Bekesy tracking and increasing contrast, were examined over 4 sessions with a sample of 12 young and 12 elderly adults. The stimuli were presented as either a static display or in counterphase at a rate of 7.5 Hz. The method of increasing contrast proved to be the more stable and reliable of the two methods. Given the superior psychometric properties of this method and its ease of administration, the method of increasing contrast is recommended as a rapid and reliable screening tool. It should be of particular use for spatial contrast sensitivity assessment of patients who have a limited attention span.

Adolescent↗
PubMed1991

Spatial contrast sensitivity in Alzheimer's disease: a comparison of two methods.

The present study was designed to compare the contrast sensitivity functions (CSF) obtained with the Nicolet CS2000 and the Vistech VCTS6500 for a sample (N = 25) of patients diagnosed with probable Alzheimer's disease (AD) and a sample (N = 25) of healthy elderly adults. With the Nicolet, CSF were determined for gratings presented under static and rapidly counterphased (7.5 Hz) conditions. All research participants were able to complete the Vistech test. However, 13.7 and 7.4% of the original samples of Alzheimer patients and healthy adults, respectively, did not yield usable data. Both test instruments showed uniformly low contrast sensitivities for the AD group. The results support the proposition that AD involves a primary visual disturbance and suggest that the Vistech chart can be used with a broader range of patients for initial screening.

Aged↗
PubMed1990

Comparison of scales used to quantitate the sense of effort to breathe in patients with chronic obstructive pulmonary disease.

Several different scaling techniques, i.e., Borg category (BC) and visual analogue (VA) scales have been used to quantitate the intensity of the respiratory sensations elicited during exercise, but their relationship is unclear. Six subjects with stable chronic obstructive lung disease (FEV1 = 1.2 +/- 0.1 SE L) simultaneously rated the sense of effort to breathe with both BC and VA scales during progressive, maximal exercise tests performed three to five times on a cycle ergometer. The VA scores correlated linearly with minute ventilation in all subjects in all trials (r = 0.98 +/- 0.01), and when converted to common units (i.e., Z scores) correlated closely with simultaneous scores obtained using the Borg scale (r = 0.99 +/- 0.01). Furthermore, VA scores varied minimally over several trials. Coefficient of variation for the maximal VA scores was 6 +/- 1%, which was similar to the variation in maximal Borg score (i.e., 3 +/- 1%). We conclude that the visual analogue scale is reproducible and correlates closely with the Borg score when scaling the sense of effort to breathe during exercise in subjects with stable chronic obstructive pulmonary disease.

Aged↗
PubMed1990

Balint's syndrome in Alzheimer's disease: visuospatial functions.

A subgroup of patients with Alzheimer's disease (AD) developed Balint's syndrome, an uncommon and incompletely understood disorder of visuospatial processing. We characterized the visuospatial features of three AD patients with Balint's syndrome and compared them to three comparably demented AD patients without this syndrome. On visuospatial tasks, the Balint patients were unable to integrate visual stimuli over space. On contrast sensitivity testing, the Balint patients had significantly decreased contrast sensitivities for low spatial frequency gratings (0.5, 1.0 and 2.0 cpd) alternated at 7.5 Hz. Furthermore, the Balint patients had left visual field attentional deficits and normal hemifield P100 visual evoked potentials. In AD, Balint's syndrome involved decreased sensitivity to low spatial frequencies necessary for global visuospatial analysis, a disturbance suggesting damage to the magnocellular visual system in the occipitoparietal association cortex and, possibly, in the optic nerves.

Aged↗
PubMed1986

Iconic memory and aging.

Previous attempts to measure the capacity of iconic memory in elderly adults have been unsuccessful, demonstrating in one case that 80% of the elderly adults tested could not perform above chance level. The present experiments illustrated that the partial report paradigm designed by Sperling (1960) could be used with elderly adults to obtain such a measure. Both the young and older adults exhibited a strong partial report superiority that declined with delays in the cue interval. The effect of the perceived organization of an array on readout from iconic memory also was examined. Contrary to Merikle (1980), the differences due to the display layout were attributed to better acuity for one type of display and not to perceptual organization factors.

Acoustic Stimulation↗
PubMed1986

Age effects on a nonverbal auditory sustained attention task.

A nonverbal auditory test of sustained attention was administered to 20 young and 20 elderly women, screened to ensure good health. Groups were matched for intelligence. Older subjects performed as accurately as younger subjects. Neither group showed increases in response latency as a function of time spent on test. Older subjects took longer to respond than younger subjects, but only for a particular combination of stimulus duration and order of presenting stimulus durations. When subjects were presented long tones first, there was no difference in response latency associated with age or stimulus duration. When short tones were presented first, older subjects were slower than younger subjects in both duration conditions and in response to long tones were slower than all other subjects.

Adult↗
PubMed1985

Aging and similarity grouping in visual search.

It has been argued that principles of perceptual organization play an important role in the representation of a visual stimulus and that elderly adults may be deficient in perceptual unit formation. The present study examined the extent to which the Gestalt principles of grouping by proximity and similarity predicted the formation of large perceptual units that could affect performance in a visual search task. The verbal reaction time to determine the presence or absence of a target letter in arrays of 1, 5, or 9 elements was determined for young (20 years) and elderly (69 years) adults. Both age groups could take advantage of the organization implied by Gestalt principles in finding a target in the context of a small implied group. The elderly adults, however, were not able to organize a single perceptual unit composed of eight elements. Thus, although the visual search performance of the age groups was similar, the elderly adults did yield evidence of a perceptual organization deficit.

Adolescent↗
PubMed1984

Stimulus parameters that produce age differences in block design performance.

Administered block designs that varied according to two parameters, Task Uncertainty and Perceptual Cohensiveness, to 83 persons 49 years of age or older. Performance was adjusted to remove motor speed differences. Performance changed significantly over the age span as a function of Task Uncertainty. From 49 years up, performance did not change as a function of Perceptual Cohesiveness. An analysis that included a group of 20 persons 30 years of age or younger yielded an interaction of Age and Perceptual Cohesiveness. From 49 years on, analytic or image segmentation processes do not seem to change, but other information processing becomes slower.

Adult↗