The contribution of covert attention to the set-size and eccentricity effects in visual search.

To reexamine the role of covert attention in visual search, the authors directly manipulated attention by peripherally cueing the target location and analyzed its effects on the set-size and the eccentricity effects. Observers participated in feature and conjunction tasks. Experiment 1 used precues, and Experiment 2 used postcues in a yes–no task under valid-, invalid-, and neutral-cueing conditions. Experiments 3 and 4 used a 2-interval alternative forced-choice visual-search task under cued and neutral conditions. Precueing the target location improved performance in feature and conjunction searches; postcueing did not. For the cued targets, the eccentricity effect for features and conjunctions was diminished, suggesting that the attentional mechanism improves the quality of the sensory representation of the attended location. The conjunction set-size effect was reduced but not eliminated. This questions serial-search models that attribute a major role to covert attention in visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The lasting effects of spike insoles on postural control in the elderly.

The purpose of the present study was to explore the lasting effects of a tactile sensitivity enhancement induced by spike insoles on the control of stance in the elderly. Healthy elderly subjects (n = 19, mean age = 68.8) and young adults (n = 17, mean age = 24.3) were instructed to stand or to walk for 5 minutes with sandals equipped with spike insoles. Postural control was evaluated four times during unperturbed stance: (1) before putting on the sandals equipped with spike insoles, (2) 5 minutes after standing or walking with them, (3) immediately after placing thin, smooth, and flexible insoles (no spike insoles) into the sandals to avoid the cutaneous contact with the spikes, and (4) after a sitting rest of 5 minutes with the no spike insoles. Sway parameters such as surface area, mean speed and root mean square were recorded. The present results suggest that (1) whatever the session (i.e. standing or walking) and the population, the artificial sensory message elicited by the spikes improved postural sway and, (2) the elderly were particularly perturbed when the tactile sensitivity enhancement device was removed. Whatever the age, the enriched sensory context provided by this tactile sensitivity enhancement device led to a better postural control; its suppression entailed a reweighting of the plantar cutaneous information. The difficulty that the elderly had to adjust the relative contribution of the different inputs probably reflected their poorer central integrative mechanisms for the reconfiguration of the postural set. A reduced peripheral sensitivity may also explain these postural deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of induced visual motion: Effects of relative position, shape, and size of the surround.

In the 1st of 3 experiments with 64 undergraduates, the induced motion perceived in a stationary central point of light was primarily determined by the movement of the outermost of 2 oppositely moving surrounds, regardless of surround shape. Exp II found that moving square surrounds were more effective than moving circular surrounds in generating induced motion. In Exp III, perceived motion of the stationary light was directly related to the size of the moving square surround. These results, which indicate that induced motion is a function of the relative position, shape, and size of the moving surround(s), may be due to changes in the observer's egocentric orientation and perception of straight ahead. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of eccentricity and spatial frequency on the orientation discrimination asymmetry

This study investigated the effects of eccentricity and spatial frequency on the discrimination of vertical and oblique (10 deg from vertical) Gabor patches. Within a display stimuli were scaled by a factor F = 1 + E/E2 at each eccentricity (E) in an attempt to equate either the number of photoreceptors (E2 = 2.5) or cortical area (E2 = 0.77) engaged at each eccentricity. The task was to detect a differently oriented target among eleven distractors. Orientation discrimination asymmetries (ODAs) were found such that an oblique stimulus was easier to detect in a background of vertical stimuli than vice versa. Subjects were equally sensitive to the two highest frequency Gabor patches and less sensitive to the lowest frequency Gabors. When stimuli were scaled with E2 = 2.5 sensitivity was constant at all eccentricities and the ODA magnitude was unaffected. When stimuli were magnified with E2 = 0.77 both sensitivity and ODA magnitude increased with eccentricity. Generally, we may conclude that the ODA effect is not a strictly foveal phenomenon nor is it a strictly high frequency effect.     

The influence of uncertainty and premovement visual information on manual aiming.

Conducted 2 experiments in which target uncertainty and the visual information available before and during a target-aiming movement were varied. 10 undergraduates participated in each of the studies. In both experiments, target uncertainty failed to interact with the visual manipulations. Findings support the idea that a visual representation contains general information about the layout of the movement environment. Data also provide evidence against the notion that a specific motor program is structured while vision is available and executed later. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of visual target and limb information on manual aiming.

Conducted 2 experiments to determine the impact of visual target information, visual limb information, and a no vision target-pointing delay on manual aiming accuracy. In Exp I, 10 undergraduates made target pointing movements with a stylus from a home switch to the center of a target pad. Movement time was recorded under different lighting conditions. In Exp II, 10 undergraduates performed the same task under stable lighting conditions. Results indicate that visual target information was more important than limb information in determining movement accuracy and demonstrate that it was not necessary for target information to be physically present, since a visual representation of the movement environment persisted for a brief period after visual occlusion. Results contradict the findings of L. G. Carlton (see record 1982-02570-001). (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationship between corneal eccentricity and improvement in visual acuity with orthokeratology

BACKGROUND: Due to the renewed attention given to reduction of myopia, interest in orthokeratology has dramatically increased. This study was performed to determine whether or not a predictor for orthokeratologic changes can be identified. METHODS: Fifteen subjects enrolled in the study. For each subject, corneal eccentricity (e) was measured, subjective refraction and autorefraction were performed, and intraocular pressures were taken. Each subject was then fitted with a rigid contact lens for orthokeratology and followed for a minimum of 16 weeks. Eleven subjects completed the study. RESULTS: No correlation between corneal eccentricity and improvement in visual acuity was found. Correlations were found between e and changes in subjective refraction, and between e and changes in autorefraction. There was also correlation between lower intraocular pressure and changes in subjective refraction, and between lower intraocular pressure and changes in autorefraction. CONCLUSIONS: These findings suggest that corneal eccentricity and lower intraocular pressures may be predictors of orthokeratologic changes. A longitudinal study with a larger subject size will be needed to conclusively determine if these two measurements are predictors of orthokeratologic changes.     

The role of peripheral and central visual information for the directional control of manual aiming movements.

Seeing one's hand in visual periphery has been shown to optimize the directional accuracy of a sweeping hand movement, which is consistent with J. Paillard's (1980; Paillard and B. Amblard, 1985) two-channels model of visual information processing. However, contrary to this model, seeing one's hand in central vision, even for a brief period of time, also resulted in optimal directional accuracy. In 3 experiments, this study tested two opposing hypotheses proposed to explain the latter finding, and also determined whether additional support could be found for the existence of a visual kinetic channel. Results indicated that seeing one's hand in central vision, even for a very short delay, resulted in the same accuracy as being permitted to see one's hand for the duration of the whole movement. This suggests that seeing one's hand around the target might enable one to code its location and that of the target within a single frame of reference and, thus, facilitate movement planning. In addition, seeing one's hand in motion while in visual periphery permitted a better directional accuracy than when this information was not available, suggesting that the movement vector, which is planned prior to movement initiation, can be quickly updated following movement initiation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric asymmetry in the visual contribution to postural control in healthy adults

This study was carried out in order to test the hypothesis of a right hemisphere dominance in the visual control of body balance. Eight healthy adults were subjected to a self-regulated lateral balance task, performed while sitting on a rocking platform. Four visual conditions were tested: open eyes with normal vision, closed eyes in the dark, left visual field-right hemisphere and right visual field-left hemisphere. Head and support displacements in the roll plane were recorded by means of an optoelectronic system. Two main results emerged from this study: (1) head stabilization in space was much more efficient in the left visual field-right hemisphere condition than in the three other visual conditions, and (2) although vision played an important role in the body stability whatever the anatomical level, there was no right hemisphere dominance at the pelvic level. A clear right hemisphere dominance was thus demonstrated as regards the visual contribution to head stabilization in space.     

Auditory and visual interactions in postural stabilization

The interaction and subsequent interpretation of sensory feedback from different modalities are important determinants in the regulation of balance. The importance of sound in this respect is not, as yet, fully understood. The aim of the present study was to determine the interaction of specific auditory frequencies and vision on postural sway behaviour. The frequencies employed represent the geometrical mean of 23 of the 25 critical bandwidths of sound, each presented at two loudness levels (70 and 90 phones). Postural sway was recorded using a biomechanical measuring platform. As expected vision had a highly significant stabilizing effect on most sway parameters. The frequency of the sound, however, appeared to influence the regulation of anteroposterior sway, while increasing loudness tended to increase mediolateral sway. At some frequencies the sound appeared to compensate for the lack of visual feedback. The interaction of sound and vision, particularly in combinations that lead to increased sway behaviour, may have implications in the occurrence, and possible prevention, of industrial accidents.     

Feature asymmetries in visual search: effects of display duration, target eccentricity, orientation and spatial frequency

In Experiments 1-3, we monitored search performance as a function of target eccentricity under display durations that either allowed or precluded eye movements. The display was present either until observers responded, for 104 msec, or for 62 msec. In all three experiments an orientation asymmetry emerged: observers detected a tilted target among vertical distracters more efficiently than a vertical target among vertical distracters. As target eccentricity increased, reaction times and errors augmented, and the set size effect became more pronounced, more so for vertical than tilted targets. In Experiments 4-7, the stimulus spatial properties were manipulated: spatial frequency; size; and orientation. The eccentricity effect was more pronounced for vertical than tilted targets and for high- than low-spatial frequency targets. This effect was eliminated when either the size, the size and orientation, or the size and spatial frequency were magnified (M-cortical factor). By increasing the signal-to-noise ratio, magnification reduced the extent of both asymmetries; it aided more the detection of tilted than vertical and of high- than low-spatial frequency targets. Experiments 4-7 indicate that performance improvement in the magnified conditions was due to the specific pairing of stimulus size with retinal eccentricity and not to the larger stimulus size of the magnified conditions. We conclude that stimulus size, orientation and spatial frequency influence the extent of the eccentricity effect and the efficiency of search performance.     

The effects of computer interface design on human postural dynamics

The main objective of this study was to examine the effects of human-computer interface design on postural dynamics, i.e., changes in working postures and postural discomfort exhibited by operators of the computer-based remote bar coding (RBC) system. In addition, the effects of different work/rest schedules on postural dynamics were evaluated. Twelve subjects participated in the laboratory experiment, which consisted of twelve scenarios utilizing two cognitive task requirement factors, i.e., (1) information presentation mode, defined through the letter image preview on the computer screen (none or one preview image); and (2) the information processing mode, defined through the specific keying method (key all characters or key 5 digits only). The third experimental factor was the work/rest schedule (50 min work/10 min break, 2 h of work/15 min break, or flexible schedule). The results showed that requirements of human-computer interface design significantly affected the operators' postural dynamics. It was concluded that not only the physical, organizational, or psychosocial work environment characteristics, but also the cognitive task characteristics are important for assessment of postural effects in the VDT work. The relationship between interface design, mental workload and postural dynamics should be carefully considered in future studies aimed at optimizing the human-computer data entry tasks.     

Planning macroscopic aspects of manual control: end-state comfort and point-of-change effects

A recent emphasis in motor control research is the planning of macroscopic features and how variables such as efficiency and comfort influence the planning process. This paper extends the work by Rosenbaum and Jorgensen (1992) by further studying the end-state comfort effect. In the first experiment, participants picked up a dowel using an underhand or overhand grip and touched one end to a numbered target on the wall. The height of the #9 target was set at the height of participants' right shoulder. The second experiment involved awkwardness ratings. Participants touched the 14 targets with the dowel as well as with a small dumbbell and the comfort of the end position was rated on a seven-point scale. In the third experiment, participants moved a dumbbell to the targets in the same procedure as the first experiment. Overall, the probability analyses indicated that as the end-state comfort effect was magnified, the sequential effect vanished and a distinct point-of-change effect appeared. Optimization theory and the knowledge model readily explained the phenomena of the end-state comfort effect, the sequential effect, and the point-of-change effect. The present findings indicate that comfort has a powerful influence on the planning of motor performance.     

Effects of sound on postural control.

Tested the assumption that due to the close association between the cochlea and the vestibular system, sounds of different frequency can affect posture in 2 experiments with 4 tones of 260, 590, 1500, and 2500 Hz. The intensity level of each tone was presented both asymmetrically and symmetrically to both ears of each of 20 21-29 yr. old Ss. In the asymmetrical study, the intensity of the right ear was held at 75 db. 2.5 db. and the left ear level was held at 95 db. 2.5 db. Analysis of variance indicates that the frequencies used did not have a significant effect on postural regulation as measured by error in postural tracking on a coordinate force platform. Results on learning of postural balance indicate that the coordinate force platform, as equipped with yoked visual feedback, can provide a most effective technique in the training of different modes of postural tracking and coordination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The gap effect during visual and auditory stimulation using manual responses

Six experiments were conducted in naive human participants to examine any facilitation produced in manual reaction time (RT) by the interposition of a temporal gap between a warning signal and an imperative signal. Peripheral visual stimuli and monoaural auditory stimuli were used as targets. Participants showed a facilitation of RTs to the targets for both auditory and visual stimuli in the five experiments in which RTs were the dependent variable. In addition, the gap effect increased over successive blocks of trials, suggesting learning. RTs were facilitated only when the gap had predictive value and was salient. Using a variable temporal gap or visual warning stimulus did not change the facilitation in RTs. A further experiment demonstrated that the gap can be perceived by the participants. The dissociation between a learned and a non-learned component in the gap effect suggests that the temporal gap induces two independent processes: warning and disengagement of attention.     

Role of eccentricity and size in the global precedence effect.

The global precedence hypothesis was investigated in a series of experirnents by considering the effects of eccentricity and size and their possible interaction on the speed of processing of both global and local levels of compound stimuli. Furthermore, the possible effect of size-eccentricity uncertainty on the temporal order of processing was examined across eccentricity. The results showed a global advantage in speed of processing regardless of experimental presentation conditions when the confound of eccentricity was controlled. Somewhat surprisingly, the pattern of response times as a function of eccentricity was quadratic. Subsequent experiments indicated that the quadratic functions obtained result from the summed individual effects of size and eccentricity. The results indicate that size and eccentricity are the main determinants of the global advantage effect and that many previous findings may be explained in terms of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus size and eccentricity in visually induced perception of horizontally translational self-motion

The effects of the size and eccentricity of the visual stimulus upon visually induced perception of self-motion (vection) were examined with various sizes of central and peripheral visual stimulation. Analysis indicated the strength of vection increased linearly with the size of the area in which the moving pattern was presented, but there was no difference in vection strength between central and peripheral stimuli when stimulus sizes were the same. Thus, the effect of stimulus size is homogeneous across eccentricities in the visual field.     

The structure of somatosensory information for human postural control

The goal of the present study was to determine the properties of the somatosensory stimulus that alter its temporal coupling to body sway. Six standing subjects were tested while touching a metal plate positioned either directly in front of or lateral to the subject. In each condition, the plate moved 4 mm at 0.2 Hz in either the medial-lateral (ML) or anterior-posterior direction (AP). The results showed that coupling between body sway and touch plate movement was strongest when the touch plate moved in a direction along the longitudinal axis of the arm. Coupling strength was weaker when the touch plate moved perpendicular to the longitudinal axis of the arm. The results consistently show that a radial expansion stimulus was more effective than a lamellar-type stimulus at the fingertip. Moreover, somatosensory information from a surface is interpreted in terms of the orientation of the contact limb and the potential degrees of freedom available through its movement.     

The effects of stochastic galvanic vestibular stimulation on human postural sway

BACKGROUND: Orthostatic hypotension (OH) predicts mortality in hypertensive persons with diabetes mellitus, but no increase in mortality has been found among random samples of home-dwelling persons with OH. We examined the risks of nonvascular and vascular deaths according to different definitions of OH among home-dwelling elderly persons. SUBJECTS AND METHODS: The study population consisted of all persons aged 70 years or older living in 5 rural municipalities (N=969), of whom 833 (86%) participated. Orthostatic tests were successfully carried out in 792 persons by nurse examiners. Orthostatic hypotension was defined as a systolic blood pressure (BP) drop of 20 mm Hg or more or a diastolic BP drop of 10 mm Hg or more 1 minute or 3 minutes after standing up. Nonvascular and vascular deaths during the follow-up period were recorded. Data on diseases, symptoms, medications, the results of clinical examinations and tests, functional ability, and health behavior were collected at the beginning of the follow-up period. RESULTS: Of the sample, 30% had OH: the prevalence of systolic OH 1 minute and 3 minutes after standing up was 22% and 19%, respectively; that of diastolic OH 1 minute and 3 minutes after standing up was 6% for each. No differences in the occurrence of nonvascular deaths were found according to any of these definitions. By Cox multivariate regression analysis, the hazard ratio of vascular death associated with a diastolic BP reduction of 1 mm Hg 1 minute after standing up was 1.02 (P=.03), adjusted for systolic BP postural changes at 1 and 3 minutes and a diastolic BP change at 3 minutes. Adjusted for other significant factors associated with vascular death, the hazard ratio for vascular death associated with diastolic OH 1 minute after standing up was 2.04 (95% confidence interval, 1.01-4.15). The corresponding hazard ratio for systolic OH 3 minutes after standing up was 1.69 (95% confidence interval, 1.02-2.80). Using a cutoff point of 7 mm Hg or greater for a diastolic BP change 1 minute after standing up, the hazard ratio for vascular death was highest: 2.20 (95% confidence interval, 1.23-3.93). By logistic regression analysis, the baseline associates of diastolic OH 1 minute after standing up were dizziness when turning the neck (odds ratio [OR], 2.44), the use of a calcium antagonist (OR, 2.31), the use of a diuretic medication (OR, 2.29), a high systolic BP (OR, 2.23), and a low body mass index (OR, 2.26). The baseline associates of systolic OH 3 minutes after standing up were male sex (OR, 1.52), diabetes mellitus (OR, 1.92), a high systolic BP (OR, 2.91), and a low body mass index (OR, 1.68). CONCLUSIONS: The presence of diastolic OH 1 minute and systolic OH 3 minutes after standing up predict vascular death in older persons. They differ from each other in their prevalence and in several associates, suggesting different pathophysiologic backgrounds. Clinicians should prescribe vasodilating and volume-depleting medications with caution for elderly persons with diastolic OH 1 minute after standing up. Appropriate treatment of hypertension might be the best means to manage the different types of OH with poor vascular prognoses.     

Detection of the sign of expansion as a function of field size and eccentricity

Detection experiments reveal that performance is decreased when the signal's spatial frequency varies unpredictably across trials compared with conditions where it is held constant. However, this effect can more or less be compensated by presenting cues shortly before each trial. To investigate the efficiency of different sensory and symbolic cue types a signal-detection experiment with spatial-frequency uncertainty was carried out. The inter-stimulus interval between cue and signal as well as for the sensory cue types, the spatial overlap between cue and signal, was varied. The results reveal appreciable efficiency differences. While some cues were only of little help, others reduced uncertainty almost entirely. However, the efficiency of cues which were identical to the signals was severely restricted by forward-masking effects when they were presented at the same position as the signal.