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PubMed1990

Effect of alcohol on visual constancy values and possible relation to driving performance.

The effects of the constancy phenomena in vision seem to be to provide information about the environment which is not solely dependent upon the characteristics of shape or size of the retinal image but which is modified by the brain to appear closer to the idealized characteristics of the real object. There is a regression away from the retinal image towards the actual object's characteristics. A plate viewed from an angle tends to look more like a disc than would be predicted from the geometry of perspective. This ability of the brain to impose conditions on perception is a high-level process which may be adversely affected by the depressive action of alcohol on the nervous system. In this case, objects such as road signs, etc. would tend to look smaller and so more distant than when sober if regression is inhibited. Drivers' reactions may be delayed if hazards are seen smaller and further away, thereby increasing the possibility of accident. This research indicates a reduction in phenomenal regression after ingestion of alcohol. There are implications for accident-rates in driving or in industry.

Adult↗
PubMed2003

Time constants in the perception of a change in the direction of motion in humans.

Motion signals are subject to spatio-temporal filtering at early stages of processing. In general, motion can be characterized by two parameters: speed and direction. This study sought to determine the time constants for the filtering of the directional component of the motion signal. In a forced-choice discrimination task, subjects were asked to choose the more abrupt change in direction of a target that moved through two 90 degrees corners. At each corner, direction of motion was low-pass filtered. Subjects were able to reliably perform this task if the filter time constants differed by >20 ms.

Choice Behavior↗
PubMed1999

Critical role of foreground stimuli in perceiving visually induced self-motion (vection).

The effects of a foreground stimulus on vection (illusory perception of self-motion induced by a moving background stimulus) were examined in two experiments. The experiments reveal that the presentation of a foreground pattern with a moving background stimulus may affect vection. The foreground stimulus facilitated vection strength when it remained stationary or moved slowly in the opposite direction to that of the background stimulus. On the other hand, there was a strong inhibition of vection when the foreground stimulus moved slowly with, or quickly against, the background. These results suggest that foreground stimuli, as well as background stimuli, play an important role in perceiving self-motion.

Adult↗
PubMed1991

The spacing illusion: a spatial aperture problem?

A geometrical illusion in which the horizontal spacing between adjacent parallel lines in a row is underestimated when the lines are tilted away from vertical in a chevron configuration was investigated in two experiments. The perceived spacing was found to decrease as the tilt angle increased, consistent with the idea that separation judgements are influenced by the normal spacing between lines ie at right angles to the line orientation. It is proposed that this illusion reveals an analogue in spatial perception to the well-known aperture problem in motion perception. In establishing the separation of nearby or overlapping shapes in an image, the visual system cannot only rely upon the normal separation of contours belonging to each shape (as would be visible through small spatial apertures or receptive fields), since this varies with contour orientation. The system is therefore faced with a spatial aperture problem. The spacing illusion may arise because information usually available to solve the problem is absent in the illusion figure, or it may reflect a bias in favour of the orthogonal, which is adopted in the face of the ambiguity.

Adult↗
PubMed1993

Optical specification of time-to-passage: observers' sensitivity to global tau.

Despite its general mathematical formulation, most empirical work on the visual perception of tau (defined as a quantity divided by its temporal derivative) has focused on the case of direct approach, with tau defined as image angle/rate of expansion. Empirical investigators tend to generalize image size analyses to off-axis approaches. However, this generalization is inappropriate for all but a few classes of objects. After mathematically reestablishing the appropriate optical cues specifying time to passage for noncollision cases, we report a series of studies in which we examined observers' sensitivities to this information in both relative- and absolute-judgment paradigms. In general, we found observers' judgments to be accurate and robust.

Adolescent↗
PubMed2002

Haptic perception of parallelity in the midsagittal plane.

Previous studies [Perception 28 (1999) 1001; Perception 28 (1999) 781] on the haptic perception of parallelity on a horizontal plane showed that what subjects haptically perceive as being parallel deviates considerably from what is physically parallel. The deviations could be described with a subject-dependent orientation gradient in the left-right direction. The gradients found in the bimanual conditions were significantly larger (about 70%) than those in the unimanual conditions. The questions to be answered in the present study are the following: (1) Does the haptic perception of parallelity in the midsagittal plane also show systematic deviations from veridicality? (2) Are the unimanual and bimanual performances again quantitatively but not qualitatively different? The set-up consisted of a plate positioned in the midsagittal plane of the subject. The subject touched the right side of the plate with his/her right hand and the left side with the left hand. The results show again large systematic deviations. The major part of the deviations can be described by means of a subject-dependent orientation gradient in the vertical direction. The quantitative (but not qualitative) difference between the unimanual and the bimanual conditions is much larger in the midsagittal plane than in the horizontal plane.

Adolescent↗
PubMed2005

Attentional modulation of electrophysiological activity in auditory cortex for unattended sounds within multistream auditory environments.

In three experiments, we addressed the issue of attention effects on unattended sound processing when one auditory stream is selected from three potential streams, creating a simple model of the cocktail party situation. We recorded event-related brain potentials (ERPs) to determine the way in which unattended, task-irrelevant sounds were stored in auditory memory (i.e., as one integrated stream or as two distinct streams). Subjects were instructed to ignore all the sounds and attend to a visual task or to selectively attend to a subset of the sounds and perform a task with the sounds (Experiments 1 and 2). A third (behavioral) experiment was conducted to test whether global pattern violations (used in Experiments 1 and 2) were perceptible when the sounds were segregated. We found that the mismatch negativity ERP component, an index of auditory change detection, was evoked by infrequent pattern violations occurring in the unattended sounds when all the sounds were ignored, but not when attention was focused on a subset of the sounds. The results demonstrate that multiple unattended sound streams can segregate by frequency range but that selectively attending to a subset of the sounds can modify the extent to which the unattended sounds are processed. These results are consistent with models in animal and human studies showing that attentional control can limit the processing of unattended input in favor of attended sensory inputs, thereby facilitating the ability to achieve behavioral goals.

Acoustic Stimulation↗
PubMedDate not supplied

[Quantitative criteria for the evaluation of congenital chromatic vision disorders].

The minimum angular size of a color stimulus required for its discrimination has been ascertained to be a quantitative criterion for evaluating the form and degree of congenital chromatic visual diseases. Unlike individuals with normal color perception who distinguish all basic and intermediate colors despite their saturation, anomalous trichromats discriminate more saturated colors with larger angular sizes of stimuli than those with normal color perception. Mild and moderate anomalous trichromats do not discriminate lowly saturated colors or for this they require the angular sizes tens of times greater those for normal trichromats. Persons with severe chromatic visual diseases (Type A) do not distinguish moderately saturated colors either. On recognizing the color of test objects, anomalous trichomats make the most mistakes in perceiving the green and yellow colors, the fewest mistakes in perceiving the red color. The minimum angular sizes required to distinguish colors, the percent of errors in their discrimination, and the range of vision of safety signs depend on the form and degree of congenital chromatic diseases. This makes it necessary to apply a differential approach to providing jobs that require rapid and accurate color discrimination in persons with the protanomalous forms of chromatic pathology.

Adaptation, Physiological↗
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↗
PubMed2004

Changes in neighborhood walking are related to changes in perceptions of environmental attributes.

BACKGROUND: Several studies have found significant cross-sectional associations of perceived environmental attributes with physical activity behaviors. Prospective relations with environmental factors have been examined for vigorous activity, but not for the moderate-intensity activities that environmental and policy initiatives are being designed to influence. PURPOSE: To examine prospective associations of changes in perceptions of local environmental attributes with changes in neighborhood walking. METHODS: Baseline and 10-week follow-up telephone interviews with 512 adults (49% men). RESULTS: Men who reported positive changes in aesthetics and convenience were twice as likely to increase their walking. Women who reported positive changes in convenience were more than twice as likely to have increased their walking. There were contrasting findings for men and women who reported traffic as less of a problem: Men were 61% less likely to have increased walking; however, women were 76% more likely to have done so. CONCLUSIONS: Further studies are needed to determine the possibly causal nature of such environment-behavior relations and to elucidate relevant gender differences. Such evidence will provide underpinnings for public health initiatives to increase participation in physical activity.

Adolescent↗
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↗