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Biomedical subjects

L A Lott

Publications and source records attributed to L A Lott.

At least 19 recordsLinked to original sources
PubMed2001

Reading performance in older adults with good acuity.

PURPOSE: This study evaluated factors affecting reading performance in a sample (N = 544) of older adults (mean age 72.8 years, range 58 to 102) with good high-contrast acuity (> or = 20/32). METHODS: Using the Pepper Reading Test, the relationship between reading rate and several vision measures was assessed. RESULTS: Mean corrected reading rate fell substantially over the age range tested despite the fact that these individuals all had good acuity. However, multiple regression analysis indicated that when other measures were taken into account (most notably, low-contrast vision, motor ability, and attentional field integrity), age was not a significant independent predictor of corrected reading rate. CONCLUSION: Reading is an important skill, and ways of enhancing reading performance should be explored. Good high-contrast acuity does not assure that older individuals can read satisfactorily.

Aged↗
PubMed2000

Ocular contributions to age-related loss in coarse stereopsis.

PURPOSE: To determine the basis for the dramatic decline in coarse stereopsis that occurs with age. METHODS: The Frisby test was used to assess stereopsis in a large sample of randomly selected persons over the age of 58 years. A number of other vision functions were also assessed in the same persons. The data were used to address the question of whether the decline in stereopsis reflects age-related alterations in cortical stereopsis mechanisms themselves (e.g., disparity detectors) or a degradation of the signal reaching the cortex as a result of alterations in earlier visual components. Two of three vision measures were binocular and thus reflect predominantly the function of the better eye. RESULTS: We find, as many others have reported, that even very coarse stereopsis declines dramatically with age. Despite not having separately assessed each eye, we find that among those selected to have good ocular function there was no significant decline in coarse stereopsis with age. CONCLUSION: These findings suggest that the enormous decline in coarse stereopsis with age can be accounted for by alterations in early stages of vision processing.

Aged↗
PubMed2000

The relation between visual acuity and other spatial vision measures.

PURPOSE: To examine to what extent measurement of standard visual acuity allows prediction of other spatial vision measures on an individual basis when high correlations exist between visual acuity and the other measures. METHODS: A series of spatial vision functions were measured in a sample of 900 community-dwelling older observers. Regression analysis was performed, and correlation coefficients were calculated between standard high-contrast visual acuity and other spatial vision measures including contrast sensitivity, low-contrast acuity, low-contrast low-luminance acuity (SKILL card), and disability glare acuity. RESULTS: All measures were highly and significantly correlated with standard visual acuity (r = 0.68 to 0.91). Despite the high correlations, many predictions of the other spatial vision measures from the correlation with standard acuity fell considerably outside of acceptable ranges determined by repeatability. The influence of the range of values in correlations is emphasized. CONCLUSIONS: Other spatial vision measures cannot be predicted on an individual basis from visual acuity despite high and significant correlations between the measures.

Aged↗
PubMed1999

Saccades reduce latency and increase velocity of ocular accommodation.

Horizontal vergence can be stimulated binocularly with disparity (disparity vergence) or monocularly with accommodation (accommodative vergence). The latter results from a neural cross-coupling that causes both horizontal vergence and accommodation to respond when either one is stimulated [Alpern, M., & Ellen, P. (1956). American Journal of Ophthalmology, 42, 289-303]. The velocity of disparity and accommodative vergence is enhanced when accompanied by saccades [Enright, J. T. (1984). Journal of Physiology (London) 350, 9-31; Enright, J. T. (1986). Journal of Physiology (London) 371, 69-89]. Based upon the coupling between accommodation and vergence, we predicted that accommodation should also be facilitated by saccades. An SRI Dual Purkinje Eyetracker was used to measure left and right eye position, and the accommodation of the left eye, in response to stimulation. Horizontal saccades were stimulated by targets separated by 2-6 degrees and accommodation was stimulated monocularly over a range of +/- 2 diopters (D). When saccades occurred within 0-400 ms following a monocular step stimulus to accommodation, latency of accommodation decreased and the associated accommodative-vergence response was synchronized with the saccade. Saccades also enhanced the velocity of accommodation and accommodative-vergence, and this facilitation increased with saccade amplitude. Transient vergence responses that are normally associated with saccades [Erkelens, C. J., Steinman, R. M., & Collewijn, H. (1989). Proceedings of the Royal Society of London B. Biological Sciences, 236, 441-465; Maxwell, J. S., & King, W. M. (1992). Journal of Neurophysiology, 68 (4), 1248-1260] did not affect accommodation when it was not stimulated by defocus. Because saccades and accommodation utilize separate plants and final common pathways, the synchronization of saccades and accommodation and the enhanced velocity of accommodation and accommodative-vergence must occur at more central sites. Possibilities include the superior colliculus, which represents both accommodation and saccades [Nagasaka, Y., & Ohtsuka, K., (1998). Investigative Ophthalmology AVRO supplement], vestibular nuclei which project to regions near the oculomotor nuclei [Lang, W., Buttner-Ennever, J. A., & Buttner, U. (1979). Brain Research, 177, 3-17], and interactions between omni pause neurons and near response cells of the mesencephalic reticular formation (MRF) [Mays, L. E., & Gamlin, P. D. R. (1995a). Current Opinions in Neurobiology, 5, 763-768; Mays, L. E., & Gamlin, P. D. R. (1995b). Eye movement research: Mechanisms, processes and applications. New York: Elsevier] which represent both accommodation and vergence [Judge, S. J., & Cumming, B. G. (1986). Journal of Neurophysiology, 55, 915-930; Zhang, Y., Mays, L. E., & Gamli, P. D. R. (1992). Journal of Neurophysiology, 67, 944-960].

Accommodation, Ocular↗
PubMed1997

The influence of subject instruction on horizontal and vertical vergence tracking.

Previously it has been reported that horizontal disparity vergence is strongly influenced by subject instructions to vary attention or tracking effort. This paper describes experiments which compared these instruction effects on horizontal and vertical disparity vergence. Within-trial comparisons were made possible by use of oblique (combined horizontal and vertical) disparity modulation. Subjects viewed a flat, fully correlated, dynamic random noise stereogram pattern through stationary circular apertures, with a small stationary fixation cross superimposed in the center. The disparity of the noise pattern was either modulated sinusoidally or changed abruptly. Subjects were instructed either to (1) hold fixation on the cross and ignore the disparity modulation of the noise pattern; or (2) follow the movement of the noise pattern as accurately as possible. Subjects showed clear effects of instruction on the horizontal component of tracking, but showed little or no effect on the vertical component. Horizontal and vertical components of oblique vergence tracking appear to be largely independent, and vertical vergence is affected minimally, if at all, by an effort to track.

Attention↗
PubMed1997

Effects of lorazepam on the distribution of spatial attention.

Reaction time (RT) to stimulus events was assessed for 2 tasks with different spatial attention demands before and after receiving either a placebo or lorazepam (1 mg). In 1 task (onset), 12 participants responded to the onset of 1 of 5 potential dot targets contained within either a small or large area. In the other task (offset), all 5 targets were illuminated and 12 participants responded to the offset of 1 of them. In the onset task, lorazepam slowed RT equally for both the large and small display areas. In the offset task, substantial impairment was found with the large but not the small display area. Results are consistent with the hypothesis that lorazepam interferes with the processes involved in the movement of spatial attention. The possibility that lorazepam selectively impairs the disengage component of attentional movement is discussed.

Adult↗
PubMed1997

The conundrum of patient records.

Examines issues and concerns surrounding the management of patient information in the form of health records, such as accessibility, privacy, security, confidentiality, ownership and eventual disposal. Discusses the effects of health reform on the management of patient information, especially regionalization in Saskatchewan, and advances in technology. Concludes that it is incumbent on health-care professionals to show leadership and set guidelines since technology will outstrip legislation.

Confidentiality↗
PubMed1996

Suppression of motion-produced smear during smooth pursuit eye movements.

Humans make smooth tracking eye movements to keep the image of a moving target on the foveal region of the retina and, thereby, maintain acute vision. Although the images of physically stationary background stimuli sweep across the retina during smooth pursuit eye movements, non-pursued targets are usually perceived to be neither moving nor smeared. The lack of perceived movement of background stimuli is generally attributed to a 'cancellation' of the retinal image motion by extraretinal information about the eye movement [1,2]; this information comes primarily from a neural facsimile of the efferent command to move the eyes, augmented by afferent signals from receptors in the extraocular muscles [3,4]. Here, we show that a physically stationary target presented during smooth tracking is perceived to have considerably less smear than a target that moves comparably across the retina, but when the eye is stationary. This result implies that extraretinal signals for pursuit eye movements also contribute to the alleviation of perceived smear for non-tracked, background targets.

Eye Movements↗
PubMed1996

An effect of alcohol on the distribution of spatial attention.

OBJECTIVE: Previous research on the effects of alcohol on visual performance led us to the prediction that alcohol should interfere with the distribution of visual spatial attention. This prediction was examined in two experiments that measured the effect of alcohol on reaction time (RT) for tasks that differed in visual spatial attention requirements. METHOD: In the first experiment, 48 adult volunteers (33 female) responded to either the onset or offset of one of five potential targets without alcohol to determine the relative demands on attention of stimulus onset and offset. The spatial extent of the five-target display was also varied. In the second experiment, the effect of alcohol was determined for both the onset and the offset tasks in 12 adult volunteers (nine female). RESULTS: The offset task was found to place greater demands on spatial attention as the increase in display area result in relatively greater increases in RT. Alcohol increased RT in the offset task for the larger, but not the smaller, display, and there were no significant effects of alcohol for the onset task. CONCLUSIONS: The results indicate that alcohol impairs performance on tasks that place greater demands on visual spatial attention and likely disrupts the ability to shift attention from one spatial locus to another during serial search.

Adolescent↗
PubMed1993

Benzodiazepine effects on flicker sensitivity: role of stimulus frequency and size.

1. Benzodiazepines (BZDs) impair sensitivity to temporally modulated visual stimuli (flicker). Critical flicker-fusion frequency (CFF) is commonly used as a measure of this effect, but it only measures sensitivity to a narrow range of frequencies, usually above 25 Hz. Are other frequencies more sensitive to the effects of BZDs? 2. Flicker sensitivity at 1, 2, 4, 8, 16, and 32 Hz was measured for 1 degrees and 5 degrees stimuli before and 50 to 100 minutes after triazolam (0.25 mg), lorazepam (1.0 mg) and placebo. Drug effects on CFF were also measured. 3. Both BZDs significantly impaired overall flicker sensitivity. Triazolam produced 50% more impairment than lorazepam. CFF was significantly impaired by triazolam. BZD effects did not vary with stimulus size. 4. Significantly greater BZD-induced impairment of flicker sensitivity occurred at 16 Hz than at 1, 2, 4, or 32 Hz. 5. The magnitude of BZD effects on flicker sensitivity vary with the temporal frequency of the stimulus. BZD effects are greatest for 8-16 Hz stimuli.

Adult↗
PubMed1993

Up-down asymmetry in vertical induced motion.

Induced motion (IM) is the illusory movement of an object in the direction opposite to the real motion of adjacent detail. One theory of IM suggests that it results, in part, from suppression of optokinetic nystagmus (OKN) by fixational (smooth-pursuit) effort. In several studies an asymmetry in human vertical OKN has been reported, with upward optokinetic stimulation eliciting higher OKN gain than downward motion. This provides a test of the nystagmus-suppression theory of IM. If suppression of OKN contributes significantly to IM, upward inducing stimuli should result in a greater magnitude of the illusion than should downward stimulus motion. Additionally, the asymmetry of vertical OKN should become more pronounced at higher stimulus velocities. Therefore, the asymmetry of vertical IM should be greater at higher inducing-stimulus velocities. Twelve subjects viewed a large, random-dot stimulus, which moved either upward or downward at a velocity of 10, 40, or 70 deg s-1. Subjects fixated a horizontally moving laser spot and adjusted a rod to match the apparent slope of the motion path of the spot. IM magnitude was derived from these measures. Mean IM velocity was significantly higher with upward than with downward stimulation, and the difference was maximal at velocities of 40 and 70 deg s-1. The results are discussed within the context of the nystagmus-suppression theory and other theories of IM.

Adult↗
PubMed1992

The relationship between vestibulo-ocular reflex plasticity and changes in apparent concomitant motion.

The vestibulo-ocular reflex (VOR) and the apparent motion of a spot stimulus fixated during head movement (apparent concomitant motion, ACM) were measured before and after an adaptation period during which subjects attempted fixation of a stimulus which moved either in the same or opposite direction as head oscillations. Movements of the head were voluntary and paced by a metronome at either 0.5 or 2.0 Hz during the 4 min adaptation period. Pre- and post-adaptation measures of VOR and ACM were obtained for both frequencies of head oscillation. VOR and ACM were altered similarly by the period of exposure to correlated head and stimulus motion. Viewing a stimulus moving in the same direction as head motion resulted in decreased VOR gain and increased ACM in the opposite direction as head motion. Viewing a stimulus moving opposite head motion resulted in increased VOR gain and increased ACM in the same direction as head movement. Differences between pre- and post-measures tended to be maximal at the adaptation frequency, but transferred to a lesser degree to the other frequency. The results indicate that changes in motor and perceptual systems are related, and are consistent with the proposal that VOR gain is a determinant of ACM.

Adaptation, Ocular↗
PubMed1991

Observations on the adaptation of induced motion.

Induced motion (IM) was measured before and after a 10-min adaptation period during which subjects viewed the IM display without judging IM magnitude. The inducing stimulus was a rectangle, which contains both horizontal and vertical reference detail. The magnitude of IM was significantly lower following the adaptation period. This result is inconsistent with the hypothesis that adaptation of IM represents an instance of perceptual learning wherein the contribution of relative motion to motion perception is reduced. In a separate study, similar results were obtained when the inducing stimulus was a single vertical bar presented either to the left or to the right of the fixation stimulus. In addition, adaptation was obtained when the location of the inducing bar was changed during test measures, demonstrating that this effect is not specific to the retinal locus of the adaptation stimulus.

Adult↗
PubMed1990

Relationship of induced motion and apparent straight-ahead shifts to optokinetic stimulus velocity.

Induced motion (IM) of a fixated spot stimulus and shifts of the apparent straight-ahead (ASA) from the objective median plane were studied as a function of the velocity of a full-field optokinetic background stimulus. Both IM and ASA were influenced similarly by changes in stimulus velocity. The magnitude of both responses, averaged across subjects, increased to a peak level with background velocities of 40-80 deg/sec and decreased at higher velocities. Individual subjects differed with respect to the precise functions by which IM and ASA shifts were related to stimulus velocity. However, for individual subjects, the effects of velocity on IM and ASA shifts were typically highly correlated. Although IM is correlated with shifts of ASA in the opposite direction, the magnitude of the ASA shift is insufficient to account for the observed IM.

Adult↗
PubMedDate not supplied

Sensitivity to full-field visual movement compatible with head rotation: variations with eye-in-head position.

Variations in velocity detection thresholds for full-field visual rotation about various axes are compatible with a simple channel-based system for coding the axis and velocity of the rotation (Harris & Lott, 1995). The present paper looks at the frame of reference for this system. The head-centered, craniotopic reference system and the retinal-based, retinotopic reference systems were separated by using eccentric eye positions. We measured the threshold for detecting full-field visual rotation about a selection of axes in the sagittal plane with the eyes held either 22 1/2 degs up, straight ahead or 22 1/2 degs down in the head. The characteristic features of the variation in detection thresholds did not stay stable in craniotopic coordinates but moved with the eyes and were constant in retinotopic coordinates. This suggests that the coding of head rotation by the visual system is in retinotopic coordinates.

Adult↗
PubMedDate not supplied

Sensitivity to full-field visual movement compatible with head rotation: variations among axes of rotation.

Movement detection thresholds for full-field visual motion about various axes were measured in three subjects using a two-alternative forced-choice staircase method. Thresholds for 1-s exposures to rotation about different rotation axes varied significantly over the range 0.139 +/- 0.05 deg/s to 0.463 +/- 0.166 deg/s. The highest thresholds were found in response to rotation about axes closely aligned to the line of sight. Variations among the thresholds for different axes could not be explained by different movement patterns in the fovea or variations in motion sensitivity with eccentricity. The variations can be well simulated by a three-channel model for coding the axis and velocity of full-field visual motion. A three-channel visual coding system would be well suited for extracting information about self-rotation from a complex pattern of retinal image motion containing components due to both rotation and translation. A three-channel visual motion system would also be readily compatible with vestibular information concerning self-rotation arising from the semicircular canals.

Adult↗