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PubMed1995

Effects of optical pitch on oculomotor control and the perception of target elevation.

In two experiments, we used an ISCAN infrared video system to examine the influence of a pitched visual array on gaze elevation and on judgments of visually perceived eye level. In Experiment 1, subjects attempted to direct their gaze to a relaxed or to a horizontal orientation while they were seated in a room whose walls were pitched at various angles with respect to gravity. Gaze elevation was biased in the direction in which the room was pitched. In Experiment 2, subjects looked into a small box that was pitched at various angles while they attempted simply to direct their gaze alone, or to direct their gaze and place a visual target at their apparent horizon. Both gaze elevation and target settings varied systematically with the pitch orientation of the box. Our results suggest that under these conditions, an optostatic response, of which the subject is unaware, is responsible for the changes in both gaze elevation and judgments of target elevation.

Adolescent↗
PubMed1990

Dissociation of short- and long-range apparent motion in visual search.

The visual search paradigm was used in four experiments to investigate apparent motion perception. The addition of distractor items led to a linear increase in reaction time under long-range (LR) conditions (greater than 35 min of arc displacement), whereas reaction time was independent of displays size under short-range (SR) conditions (less than 18 min of arc). Although clear performance differences were obtained, Ss had difficulty in distinguishing between the two types of apparent motion displays when asked to make such judgments (Experiment 2). Experiments 3 and 4 explored some variables that may constrain the search process. Search times under LR conditions were reduced when some of the distractors were stationary or the motion of the distractors was homogeneous. Form and motion were found to be separable, whereas color and motion were not. Varying the color (and brightness) interfered with the processing of motion information.

Adult↗
PubMed1993

Auditory looming perception: influences on anticipatory judgments.

Several studies in the auditory-perception literature hint that listeners may be able to anticipate the time of arrival of an approaching sound source. Two experiments are reported in which listeners judged the time of arrival of an approaching car on the basis of various portions of its auditory signal. Subjects pressed a computer key to indicate when the car would have just passed them, assuming that the car maintained a constant approach velocity. A number of variables were tested including (a) the time between the offset of the signal and the virtual time of passage, (b) duration of the signal, and (c) feedback concerning judgment accuracy. Results indicate that increasing the time between signal offset and virtual time of passage decreases judgment accuracy whereas the actual duration of the signal had no significant effect. Feedback significantly improved performance overall.

Adult↗
PubMed1995

Perceptual and cognitive processes in time-to-contact estimation: analysis of prediction-motion and relative judgment tasks.

Three classes of task appear to involve time-to-contact (TTC) information: coincidence anticipation (CA) tasks, relative judgement (RJ) tasks, and interceptive actions (IAs). An important type of CA task used to study the perception of TTC is the prediction-motion (PM) task. The question of whether it is possible to study the perceptual processes involved in the timing of IAs using PM and RJ tasks is considered. A revised version of the tau hypothesis is proposed as an account of the perceptual information processing involved in the control of fast IAs. This draws on the distinction between "motor" and "cognitive" visual systems. It is argued that task variables affect whether "cognitive" information processing is involved in performance and can determine whether TTC information is used at all. Evidence is reviewed that suggests that PM and RJ tasks involve cognitive processing. It is argued that target viewing time, TTC at response initiation, amount of practice, and whether there is a period between target disappearance and response are task variables that determine whether cognitive processing will influence responding.

Attention↗
PubMed1987

Asymmetric processing in perception of apparent movement.

Asymmetric processing of movement-simulated spatial arrays was studied by the method of successive random presentation to the left or right visual half-field. On each trial two arrays consisting of between 2 and 5 dots were tachistoscopically presented in rapid succession to one visual half-field, in such a way as to simulate movement of the dots. Subjects' response choice represented a presumed continuation of the apparent movement. This was assumed to involve a process of prediction in that subjects inferred the trajectory of the stimulus dots in order to choose a response array. Response accuracy, which was measured by the number of correct response arrays chosen from a three-array series on each trial, was greater when dot arrays were presented to the left visual half-field than when they were presented to the right half-field. It was concluded that the right hemisphere of the brain plays an important role in processing for this task, and task features that may be attributed to right hemisphere processing were discussed.

Adult↗
PubMed1995

Local and global processes in surface lightness perception.

Various demonstrations show that a target of constant luminance can be made to appear darker in perceived lightness merely by introducing an adjacent region of higher luminance. This has often been interpreted as a manifestation of contrast effects produced by lateral inhibition, a relatively local process. An alternative interpretation holds that the highest luminance in such a display serves as an anchor that defines the white level. This interpretation is global in the sense that the anchor need not be located near any particular target in order to serve as its standard. Edge integration processes have been postulated that would enable such remote comparisons, but there is controversy about the strength of these processes. We report a series of experiments in which local and global processes were assessed. Specifically, we tested whether the introduction of a higher luminance has a greater darkening effect on an adjacent target than on a remote target. We found no difference, suggesting that the darkening effect is a matter of anchoring, not contrast, and that edge integration processes required by anchoring are relatively strong.

Attention↗
PubMed1978

Comparison of the visual perception of a runway model in pilots and nonpilots during simulated night landing approaches.

Relative motion parallax, a cue that can contribute to visual judgments of glide path angle, was studied for its effect on simulated nighttime approaches in two experiments: 1) 16 pilots and 16 nonpilots adjusted the slant of a model runway to make it appear horizontal under nighttime conditions on both dynamic trials, as the model approached them, and on static trials, with the model stationary; 2) 12 pilots and 12 nonpilots performed the same task in dynamic trials while viewing the model in a dark field as before, and while viewing the model within a window which provided a stable visual frame of reference. Neither flying experience nor the visual frame of reference enhanced sensitivity to relative motion parallax. However, some errors were smaller in pilots, indicating that flying experience enhances other runway images cues. Direct judgments of approach angle magnitude indicated overestimation by an approximate factor of 2. These findings indicate large visual illusions in the nighttime situation and suggest that the ineffectiveness of relative motion parallax may be an important part of night approach problems.

Adolescent↗
PubMed2002

Illusions in action: consequences of inconsistent processing of spatial attributes.

Many authors have performed experiments in which subjects grasp objects in illusory surroundings. The vast majority of these studies report that illusions affect the maximum grip aperture less than they affect the perceived size. This observation has frequently been regarded as experimental evidence for separate visual systems for perception and action. In order to make this conclusion, one assumes that the grip aperture is based on a visual estimate of the object's size. We believe that it is not, and that this is why size illusions fail to influence grip aperture. Illusions generally do not affect all aspects of space perception in a consistent way, but mainly affect the perception of specific spatial attributes. This applies not only to object size, but also to other spatial attributes such as position, orientation, displacement, speed, and direction of motion. Whether an illusion influences the execution of a task will therefore depend on which spatial attributes are used rather than on whether the task is perceptual or motor. To evaluate whether illusions affect actions when they influence the relevant spatial attributes we review experimental results on various tasks with inconsistent spatial processing in mind. Doing so shows that many actions are susceptible to visual illusions. We argue that the frequently reported differential effect of illusions on perceptual judgements and goal-directed action is caused by failures to ensure that the same spatial attributes are used in the two tasks. Illusions only affect those aspects of a task that are based on the spatial attributes that are affected by the illusion.

Cues↗
PubMed1980

Perception of relative velocity: a revision of the hypothesis of relational determination.

The conventional formulation of the hypothesis of relational determination asserts that the perceived relative velocities of two or more objects depend upon their relative rates of displacement with respect to stationary referents in the visual field. Experiment 1 showed that this formulation is too restrictive by demonstrating the transposition-of-velocity effect under conditions in which two light spots moved in the absence of static visible contours and traversed unequal path lengths. Experiment 2 showed that angular velocity per unit of relative angular extent, and not relative linear or perceived extent, of the respective motion paths influences perceived relative velocity in nonarticulated space. The retinal dimensions of static visible frameworks were shown in experiment 3 to influence perceived relative velocity in a direction consistent with the conventional formulation of the relational-determination hypothesis, but the weight of the evidence suggested a reformulation along the following lines: the perceived relative velocities of two objects are significantly affected by the proportions of the retinal projections of the respective movement fields traversed by the two objects in the same unit of time, even when the motion fields consist only of the objects' motion paths.

Discrimination Learning↗
PubMed2003

Cognitive styles: errors in directional judgments.

Previous studies on spatial memory have shown that, in judging direction, participants are more accurate and faster when a map is aligned with the perspective of the spatial layout they had learned (alignment effect). Rossano and Warren (1989 Perception 18 215-229) have shown that when participants have to do a contra-aligned judgment they can either answer correctly, or make alignment or mirror-image errors. We think that the kind of response depends on the different way in which people acquire environmental knowledge: landmark, route, and survey. We hypothesise that landmark and route participants show alignment effects and make, respectively, alignment errors and mirror-image errors, whereas survey participants do not show an alignment effect. An experiment is reported in which participants performed three tasks in order to distinguish their cognitive style. We selected thirty landmark, thirty route, and twenty-eight survey participants. They were then submitted to directional judgment tasks to verify whether the alignment effect was present and to observe the kind of responses. The results revealed that survey participants did not show an alignment effect, and that the kind of errors could depend on the directional judgment task participants had to do, and not only on the cognitive style.

Adult↗
PubMed1991

[Invariance in relation to transformations: a comparison of space perception and imagined space].

The present paper is based on the assumption of a functional equivalence between the processes of perception and imagination and a functional isomorphism between physical and phenomenal relations. The intention is to look for systematic deviations between 'measured', 'perceived' and 'imagined' space. Therefore a room was equipped with 32 pieces of furniture, giving it the appearance of a combined library and study room. A miniature model (1:10) of the room was constructed. In a two-factorial design with 10 experimental conditions, subjects performed model-reconstructions. The first factor refers to cognitive modality and represents different amounts of information of the physical layout, the endpoints of the continuum being 'complete insight' and 'no insight'. The second factor is a rotation of the model during the reconstruction (0 degrees vs. 180 degrees). Data analysis is based on location and orientation measures of the objects and distinguishes between 'semantic' and 'geometric' errors. The main results are: Even under conditions of only partial insight the spatial relations of the missing objects can be consensually reconstructed. While the absolute amount of the reconstruction errors largely depends on the two factors (modality and rotation), substantial relations of the original room are preserved under the different experimental conditions. The results are in good accordance with the assumption of functional equivalence and are critically discussed with respect to the concept of functional isomorphism.

Adult↗
PubMed1989

The consistency of element transformations affects the visibility but not the direction of illusory motion.

Two experiments tested whether the consistency of element transformations affected perceptions of long-range apparent motion. Vertical lines were used to generate apparent motion against one of two different backgrounds, control and depth. Consistency was manipulated by changing the size of the vertical lines. In some displays, the size of the vertical lines remained constant during movement. In other displays, the size of the vertical lines changed during movement. Consistent movement occurred when the size manipulation was in agreement with the type of background used. In Experiment I, points of subject equality for the quality of motion relative to a standard display were measured. These PSEs indicated that consistent movement (e.g., line sizes held constant for control background displays) was more visible than inconsistent movement (e.g., line sizes constant for depth background displays). In Experiment II, a motion competition display was used to measure thresholds for perceived direction of motion. The depth background was used to make motion in one direction more consistent than motion in the opposite direction. However, no significant differences were noted between thresholds obtained in this condition and those obtained in a control condition. Thus the consistency of element transformations affected the quality of motion, but did not affect the perceived direction of motion. These results are consistent with Ullman's (The Interpretation of Visual Motion, MIT Press, 1979) two-component theory of apparent motion.

Distance Perception↗
PubMed2001

Interactions among end-effectors and movement parameters influence reaction time in discrete, rapid aimed movements.

Two reliable findings in discrete, rapid aimed movements are that reaction time increases with decrease in target diameter (for the short-length movements), and reaction time is not affected by movement length [Journal of Experimental Psychology, Human Perception and Performance 104 (2) (1975) 147]. Participants normally use a short stylus (SS) to tap targets located on either side of a central (aligned with body midline) start-point with no restrictions imposed on the initial posture of the limb or segmental recruitment except as determined by movement conditions. Thus, the effects of movement parameters on reaction time in previous work are potentially confounded with the effect of initial posture of the limb at the start-point, along with order and amount of the contribution of segments recruited in response execution. Two experiments were performed to resolve the confounding between initial posture and recruitment of limb segments. In the first experiment a conventional stylus (pen-like) was employed and the starting position of the limb was aligned either with the body midline or with the participant's right shoulder. The effect of starting position on reaction time was not significant. In the second experiment the starting position was in line with the right shoulder. Two groups participated. One group used a conventional stylus. For the second group a modified (lengthened) stylus was used that permitted initial limb posture and number of limb segments recruited to be held constant across an extended range of movement lengths. When similar sets of limb segments were used, reaction time increased with decreasing movement length and diminishing target diameter. These findings suggest that uncontrolled initial limb posture, uncontrolled order of joint(s) recruitment, and the subsequent inclusion of reaction time values from incompatible sources may, in the final analysis, have confounded previous work investigating movement amplitude and target diameter effects on reaction time.

Adult↗
PubMed2002

Exploring the syndrome of spatial unilateral neglect through an illusion of length.

Both a neuropsychological syndrome (unilateral spatial neglect) and a visual illusion of length (the Brentano version of the Müller-Lyer illusion) bring about a misjudgement of the subjective centre of a horizontal line, with a unilateral shift. In experiment 1 we investigated, in patients with left unilateral neglect, illusory effects of horizontal length, with the aim of exploring the functional and neural basis of horizontal space perception, and the role of visual processing in shaping the patients' bisection performance. Fourteen right-brain-damaged patients with left spatial unilateral neglect, seven with and seven without left visual half-field deficits (assessed by confrontation, perimetry, and visual event-related potentials), entered this study. Two conditions of manual line bisection were assessed: setting the mid-point of a horizontal line, and of the shaft of the Brentano-Müller-Lyer illusion, with either a left- or a right-sided expansion. Both groups of patients set the subjective midpoint to the right of the objective centre of the line, consistent with the presence of left neglect. Patients with neglect and left hemianopia showed no illusory effects and a greater bisection error. The effects of the illusion, by contrast, were fully present in neglect patients without hemianopia, in both illusory conditions, adding to, or subtracting from, the rightward bisection bias. Anatomoclinical correlations revealed an association of damage to the occipital regions with the lack of illusory effects. Conversely, more anterior damage, sparing these regions, did not disrupt the illusion, revealing a dissociation between visual and spatial processing of extension. These findings suggest that processing of the Müller-Lyer illusion of length is likely to occur in the occipital cortex, at a retinotopic level of representation. In neglect patients with left homonymous hemianopia the visual deficit adds to the spatial bias, yielding a greater error in line bisection, but not in other visual exploratory tasks, such as cancellation, where the contribution of retinotopic frames is likely to be comparatively minor. Experiment 2 showed preserved illusory effects in patients with homonymous visual field defects without spatial unilateral neglect, suggesting that preserved spatial processing may compensate for unilateral visual field defects.

Adult↗
PubMed2001

Expertise and the perception of kinematic and situational probability information.

Two experiments were conducted on the nature of expert perception in the sport of squash. In the first experiment, ten expert and fifteen novice players attempted to predict the direction and force of squash strokes from either a film display (occluded at variable time periods before and after the opposing player had struck the ball) or a matched point-light display (containing only the basic kinematic features of the opponent's movement pattern). Experts out-performed the novices under both display conditions, and the same basic time windows that characterised expert and novice pick-up of information in the film task also persisted in the point-light task. This suggests that the experts' perceptual advantage is directly related to their superior pick-up of essential kinematic information. In the second experiment, the vision of six expert and six less skilled players was occluded by remotely triggered liquid-crystal spectacles at quasi-random intervals during simulated match play. Players were required to complete their current stroke even when the display was occluded and their prediction performance was assessed with respect to whether they moved to the correct half of the court to match the direction and depth of the opponent's stroke. Consistent with experiment 1, experts were found to be superior in their advance pick-up of both directional and depth information when the display was occluded during the opponent's hitting action. However, experts also remained better than chance, and clearly superior to less skilled players, in their prediction performance under conditions where occlusion occurred before any significant pre-contact preparatory movement by the opposing player was visible. This additional source of expert superiority is attributable to their superior attunement to the information contained in the situational probabilities and sequential dependences within their opponent's pattern of play.

Adolescent↗
PubMed1979

Visual-motor adaptation. Quantitative demonstration in patients with posterior fossa involvement.

Short-term visual-motor adaptation to magnifying spectacle lenses was studied in normal subjects and in patients with nonacute posterior fossa lesions. When normal subjects, looking through magnifying lenses, pointed open loop to targets without viewing their hands, they initially underestimated the distance (magnification effect). After a 20-minute close-loop training or adaptation exposure period during which they viewed the performance of their hands, a modified visual-motor scheme evolved, compensating for about half of the lens-induced pointing error (adaptation effect). Removal of the lenses after adaptation caused open-loop, overshooting pointing errors (adaptation after-effect). Four patients with remission of cerebellar signs showed normal visual-motor adaptive performance, evidence of ability to recalibrate gain. One patient with persisting cerebellar ataxia was unable to recalibrate gain during close-loop visual-motor training. His history of transient palatal myoclonus implicates a role for the cerebellar-olivary system in calibration of visual-motor gain.

Adaptation, Ocular↗
PubMed1984

Clinical performance of a disability glare tester.

A glare tester was described previously and was found, in the presence of cataracts, to be almost twice as predictive as was Snellen measurement for determining visual acuity outdoors. The current study tests the reproducibility of glare test scores and the influence of refractive error and contrast sensitivity on such scores when used in a clinical environment. Although the effects of visual acuity and impaired contrast sensitivity were found to be statistically significant components of glare test scores, the magnitudes of their effects were found to be clinically insignificant. Sequential retesting of physiologically stable eyes or, in the case of progressive cataracts, within intervals short enough to preclude discernible lenticular changes indicated that, for the most part, reproducibility of glare testing was comparable to that of visual acuity testing.

Adult↗