Age-related changes in contrast sensitivity in central and peripheral retina

Eight young (average age 20.4 years) and eight elderly (average age 64.4 years) observers took part in three experiments designed to study age-related changes in peripheral retinal function. A further eight young (average age 22.3 years) and eight elderly (average age 63.8 years) observers took part in a replication of experiment 3. All observers had normal or better-than-normal visual acuity and no evidence of ocular pathology. All testing was monocular and the eye with better visual acuity was used. In the first experiment contrast sensitivity was measured in central retina and 10 deg temporally, at spatial frequencies of 0.2, 0.8, 2.0, and 5.0 cycles deg-1. Young observers had better contrast sensitivities than older observers, but only at higher spatial frequencies (2.0 and 5.0 cycles deg-1). For both groups, contrast sensitivity was poorer with peripheral presentation of stimuli than with central presentation, but not for the lowest spatial frequency used (0.2 cycle deg-1). In the second experiment observers had to detect the presence of a sharp edge (square-wave luminance profile), while in the third and fourth experiments the target was a "fuzzy' edge (sine-wave profile). Edges were again presented centrally or 10 deg temporally. As expected from the data of experiment 1, young observers were better able to detect the sharp edge than were the older observers in both central and peripheral viewing conditions. For both age groups, edge detection was better during central viewing than during peripheral viewing. However, contrary to expectations based on the results of experiment 1, detection of the fuzzy edge was better for central than for peripheral viewing for both age groups in experiments 3 and 4. The apparent (and expected) equality of performance found in experiment 3 for young and elderly observers in detecting the fuzzy edge was shown to be due to the range of contrast values used. When appropriate contrast values were used in experiment 4, young observers detected fuzzy edges presented in central retina better than did elderly observers. The results of experiment 1 show sparing of the ability to process low spatial frequencies across (i) age and (ii) retinal location, and are discussed in terms of the notion of (i) models of age-related loss of visual function and (ii) cortical magnification. The results of experiments 2, 3, and 4 provide some support for the proposition that the contrast sensitivity of observers may be used to predict their performance on other visual tasks.(ABSTRACT TRUNCATED AT 400 WORDS)     

Functional visual field in a rapid serial visual presentation task

Dynamic temporal change in the size of functional visual field was measured using a dual task: a peripheral task in which one square in a background pattern of squares was changed in shape to a dot; and a central task involving the rapid serial visual presentation of a sequence of letters (RSVP task). The temporal lag between the occurrences of the dot and the RSVP target was manipulated. University students were asked to detect the dot and to depress a mouse button as quickly as possible while searching for the RSVP target among a sequence of distracter letters. The abrupt change in the shape of a background square in the peripheral task caused a processing deficit in the RSVP task at relative lags from –3 to –1 (255 ms to 85 ms before presentation of the RSVP target), but the encoding and retaining processes involved in identifying the RSVP target did not impair the detection of the peripheral dot. The functional visual field was found to expand while participants were performing the dual task, suggesting that preattentive detection is affected by general attentional activity.     

Newborns' central vision: Whole or hole?

We studied visual detection in 150 infants, 1- to 7-days old, by presenting single lines varying in width and location. We found that newborns detected a line only 8′ wide in the central visual field. Peripherally, they appeared to detect lines of 33′, 33′, and 1°6′ at 10°, 20°, and 30°, respectively. Thus, both the central retina and the peripheral retina appear to function at birth.     

Plasma anticholinergic activity and cognitive function in geriatric patients

This study evaluated the putative impact of circulating anticholinergic equivalents on cognitive functional performance in non-demented geropsychiatric inpatients. Standard rating instruments were administered to measure memory functions, concentration and overall functional competency. Anticholinergic plasma activity was assayed, using a radioreceptor technique with tritiated quinuclidinyl benzilate as the active reagent. None of the cognitive tests employed indicated a statistically significant change in the subjects' quantifiable level of cognitive performance. All changes in anticholinergic activities were related to adjustments in psychotherapeutic medications. The possible role of reversal of pseudodementing features is discussed as well as the potential for monitoring anticholinergic activity when treating elderly individuals with more than one centrally active medication having anticholinergic properties.     

Relation between flicker fusion threshold and retinal positions

The critical flicker frequencies (CFF) were determined for various locations on the retina. Under the conditions in which pupil size varies little with target luminance and size for a retinal location, two findings were obtained. First, the relation between the CFF value and the retinal location depends basically upon the density distribution of the receptor cells (cones and rods) on the retina. Second, when a large test field is employed, the peripheral area shows a maximal CFF value. These characteristics are explicable in terms of the retinal structure and by assuming some functions for it.     

The effect of central and peripheral field stimulation on the rise time and gain of human optokinetic nystagmus

We wished to examine the spatial (gain) and temporal (rise time) properties of human optokinetic nystagmus (OKN) as a function of stimulus velocity and field location. Stimuli were either M-scaled random dots or vertical stripes that moved at velocities between 20-80 deg s(-1). Three field conditions were examined: full field; a 20 deg central field; and a 12.5 deg central-field mask. OKN gain was found to be significantly affected by stimulus velocity and stimulus location, with the higher stimulus velocities and the 12.5 deg central-field mask giving lower gains. Steady-state gains for all three field conditions were not found to be affected by prior adaptation to stationary or moving stimuli. The 63% rise time was found to be significantly affected by the stimulus velocity, whereas this was not the case for the 90% rise time. Neither rise time was found to be significantly affected by the field location. These results indicate that, although the effectiveness (gain) of peripheral retina is lower than that of the central retina during optokinetic stimulation, the peripheral retina has access to common mechanisms responsible for the fast component of OKN.     

Responses to Optical Looming in the Retinal Center and Periphery

Stoffregen (1985, 1986) found that the periphery of the retina is insensitive to radially structured optic flow specifying postural sway. This raised the issue of whether the retinal periphery is sensitive to radially structured flow per se, that is, to radial flow specifying events other than postural sway. In the experiment discussed herein we addressed this question in the context of optical looming. Computer-generated optical displays were presented to the retinal center or periphery of standing participants, who were required to dodge out of the path of the depicted object at the last moment before impact. Depicted trajectories were slightly eccentric, requiring participants to employ a directional response. Results showed that the trajectory and time-to-contact of the simulated object strongly influenced responses for peripheral as well as central looms. In general, responses to peripheral looms closely matched those to central looms. These findings indicate that the periphery of the retina is sensitive to optically specified time-to-contact, despite the fact that such information is carried in radially structured flow patterns. We argue that impending collision and postural sway can be distin- guished on the basis of dynamics that are characteristic of each event.     

Age differences in the maintenance and restructuring of movement preparation

In 2 experiments, elderly and young subjects performed simple reaction time, choice reaction time, and movement plan restructuring tasks, using a stimulus precuing paradigm. In Experiment 1, the precue display (200 ms) and preparation interval (250, 500, 750, or 1,000 ms) were experimentally determined. In Experiment 2, the precue display interval was subject determined. For the restructuring task, the precue specified the response on 75% of the trials, enabling movement plan preparation with respect to movement parameters of arm and direction. On remaining trials, the precue incorrectly specified the response, requiring movement plan restructuring. Elderly, but not young, subjects restructured a movement plan for direction more quickly than for arm or for both parameters. These findings indicate that elderly individuals have poorer movement plan maintenance for direction than for arm and thus exhibit functional change in movement preparation processes relative to young individuals.     

Measurement of auditory cues in drivers' distraction

A driving simulator was used to examine the effects on driving performance of auditory cues in an in-vehicle information search task. Drivers' distraction by the search tasks was measured on a peripheral detection task. The difficulty of the search task was systematically varied to test the distraction caused by a quantified visual load. 58 participants completed the task. Performance on both search tasks and peripheral detection tasks was measured by mean response time and percent error. Analyses indicated that in-vehicle information search performance can be severely degraded when a target is located within a group of diverse distractors. Inclusion of an auditory cue in the visual search increased the mean response time as a result of a change in modality from auditory to visual. Inclusion of such an auditory cue seemed to influence distraction as measured by performance on the peripheral detection task; accuracy was lower when auditory cues were provided, and responses were slower when no auditory cues were provided. Distraction by the auditory cue varied according to the difficulty of the search task.     

Functional balance and dual-task reaction times in older adults are improved by virtual reality and biofeedback training.

Virtual reality (VR) training has been used successfully to rehabilitate functional balance and mobility in both traumatic brain injury (TBI) survivors and elderly subjects. Similarly, computer-based biofeedback (BF) training has resulted in decreased sway during quiet stance and decreased reaction times during a dual-task reaction time paradigm in elderly subjects. The objective of this study was to determine the effect of VR and BF training on balance and reaction time in older adults. Two groups of twelve healthy older adults completed 10-week training programs consisting of two 30-min sessions per week. VR training required that participants lean sideways to juggle a virtual ball. Participants in the BF group viewed a red dot representing their center of gravity on a screen and were required to move the dot to the four corners of the monitor. Measures of functional balance and mobility (Community Balance and Mobility Scale [CB&M]), sway during quiet stance, and reaction time during a dual task paradigm were recorded before training, as well as 1 week and 1 month after the end of the program. Both groups showed significant improvements on the CB&M, as well as decreased reaction times with training. Postural sway during quiet stance did not change significantly.     

Remapping versus short-term memory in visual stability across saccades

Saccadic eye movements cause displacements of the image of the visual world projected on the retina. Despite the ubiquitous nature of saccades, subjective experience of the world is continuous and stable. In five experiments, we addressed the mechanisms that may support visual stability: matching of pre- and postsaccadic locations of the target by an internal copy of the saccade, or retention of the visual attributes of the target in short-term memory across the saccade. Healthy human adults were instructed to make a saccade to a peripheral Gabor patch. While the saccade was in midflight, the patch could change location, orientation, or both. The change occurred either immediately or following a 250-ms blank during which no visual stimuli were available. In separate experiments, subjects had to report either whether the patch stepped to the left or right or whether the orientation rotated clockwise or counterclockwise. Consistent with previous findings, we found that transsaccadic displacement discrimination was enhanced by the addition of the blank. However, contrary to previous findings reported in the literature, the feature change did not improve performance. Transsaccadic orientation change discrimination did not depend on either an irrelevant temporal blank or a simultaneous irrelevant target displacement. Taken together, these findings suggest that orientation is not a relevant visual feature for transsaccadic correspondence.     

Eye movements during change detection: implications for search constraints, memory limitations, and scanning strategies

Search, memory, and strategy constraints on change detection were analyzed in terms of oculomotor variables. Observers viewed a repeating sequence of three displays (Scene 1-->Mask-->Scene 2-->Mask...) and indicated the presence-absence of a changing object between Scenes 1 and 2. Scenes depicted real-world objects arranged on a surface. Manipulations included set size (one, three, or nine items) and the orientation of the changing objects (similar or different). Eye movements increased with the number of potentially changing objects in the scene, with this set size effect suggesting a relationship between change detection and search. A preferential fixation analysis determined that memory constraints are better described by the operation comparing the pre- and postchange objects than as a capacity limitation, and a scanpath analysis revealed a change detection strategy relying on the peripheral encoding and comparison of display items. These findings support a signal-in-noise interpretation of change detection in which the signal varies with the similarity of the changing objects and the noise is determined by the distractor objects and scene background.     

Cross-modal detection using various temporal and spatial configurations

To better understand temporal and spatial cross-modal interactions, two signal detection experiments were conducted in which an auditory target was sometimes accompanied by an irrelevant flash of light. In the first, a psychometric function for detecting a unisensory auditory target in varying signal-to-noise ratios (SNRs) was derived. Then auditory target detection was measured while an irrelevant light was presented with light/sound stimulus onset asynchronies (SOAs) between 0 and ±700 ms. When the light preceded the sound by 100 ms or was coincident, target detection (d') improved for low SNR conditions. In contrast, for larger SOAs (350 and 700 ms), the behavioral gain resulted from a change in both d' and response criterion (β). However, when the light followed the sound, performance changed little. In the second experiment, observers detected multimodal target sounds at eccentricities of ±8°, and ±24°. Sensitivity benefits occurred at both locations, with a larger change at the more peripheral location. Thus, both temporal and spatial factors affect signal detection measures, effectively parsing sensory and decision-making processes.     

Two spatially separated attention systems in the visual field: evidence from inhibition of return

It has been demonstrated that the human visual field shows some functional inhomogeneities, in particular when the central and perifoveal regions are compared to the more peripheral regions. The present study examined this inhomogeneity by examining the effect of stimulus eccentricity on inhibition of return (IOR), a phenomenon that biases our attention towards novel locations against returning it back to previously attended locations. Eighteen subjects were examined in a visual detection task, in which a target appeared randomly following a nonpredictive spatial cue in the visual field. The eccentricities of the cues and targets were systematically manipulated from 5° to 30° with 5° increments. Results showed that response times to targets that appeared at cued locations were significantly slower than those at uncued locations for all stimulus eccentricities, demonstrating the IOR effects. However, response times at cued locations increased significantly when stimulus eccentricity shifted from 15° to 20°, leading to a much stronger IOR effect at more peripheral regions compared to central and perifoveal regions, indicating a functional dissociation between these two regions of the visual field. Possible neural mechanisms underlying this dissociation are discussed, and two attention systems modulating the two functional regions of the visual field are put forward to best account the present finding implicating in particular midbrain mechanism.     

Perceived activity and functional capacity in a rural elderly population.

This research examined 65 rural elderly residents' perception of their physical activity as compared to their functional capacity. Men's, but not women's, perceptions of their physical activity were correlated with their functional capacity.     

Roll vection analysis of suggestion-induced visual field narrowing

Instructions to simulate visual field narrowing resulted in apparently narrow visual fields when these were evaluated by means of conventional perimetry. However, when a pattern of stripes moving around the visual axis was viewed, the magnitude of the induced change in the subjective horizontal or vertical (roll vection) was unaffected. These results demonstrate that conventional perimetric techniques may in some instances be inadequate to demonstrate functional peripheral vision. Evaluation of the peripheral visual field in perimetry, the role of peripheral vision in visually guided behavior, and the effect of stressors on peripheral visual functions are discussed.     

时间对犯罪隐藏信息记忆的影响

记录模拟犯罪者和阅读报纸后对案件知情的无辜者接受隐藏信息测试时的皮肤电活动,探讨时间对犯罪隐藏信息记忆的影响。结果发现：(1)延迟条件下,模拟犯罪组的再认率和皮肤电活动变化显著高于知情无辜组,但两组在立即条件下无差异;(2)知情无辜组在延迟条件下的甄别率显著低于立即条件下,而模拟犯罪者在两种条件下无差异。结果表明,延迟测试比立即测试更容易区分模拟犯罪组和知情无辜组;犯罪甄别率在延迟条件下减少,但也减少了知情无辜者被判断为犯罪者的风险。     

Age differences in target identification as a function of retinal location and noise level: examination of the useful field of view

Foveal and peripheral target detection were compared in young adults (M age = 22 years) and older adults (M age = 66 years) who were optically corrected for the viewing distance. In a two-alternative, forced-choice task, target letters were presented at 0 degree to 10.5 degrees from fixation. Targets were presented alone, flanked on each side by one noise element (i.e., nontarget letter), or embedded in a horizontal row of 19 noise elements. An Age X Noise Level X Location interaction was obtained, wherein age differences were largest for peripheral targets presented in noise. Slope analyses of latency data showed that the performance of young adults in the high-noise condition was most similar to that of older adults in the low-noise condition. At the functional level, results indicated that aging is associated with a restricted useful field of view. In addition, the data suggest that age differences in search can be described by a model in which older adults take smaller perceptual samples from the visual scene and scan these samples more slowly than do the young adults.     

Effect of altered surfaces on postural sway characteristics in elderly subjects

Mobility is essentially based on successful balance control. The evaluation of functional strategies for postural stability is requisite for effective balance rehabilitation and fall prevention in elderly subjects. Our objective was to clarify control mechanisms of different standing positions reflecting challenges of typical everyday life situations. For this purpose, elderly subjects stood on different surfaces resulting in a change of the biomechanical constraints. Sway parameters out of time and frequency domain were calculated from center-of-pressure (COP) excursions. Besides the classic quantification of the amount of sway variability, we investigated the temporal organization of postural sway by means of nonlinear time series analysis. Limb load symmetry was quantified via foot pressure insoles. We found task dependent motor outputs: (1) asymmetrical loading in all conditions; (2) altered amount and structure of COP movements with dissimilar changes in medio-lateral and anterior–posterior direction; (3) changes of the motor output affect several time scales especially when standing on a balance board or with one foot on a step. Our results indicate that elderly subjects preferred forcefully one limb which supports a step-initiation strategy. Modifications of the postural sway structure refer to the interaction of multiple control mechanisms to cope with the altered demands. The identification of postural strategies employed in daily activities augments the ecological validity of postural control studies.