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PubMed1979

Texture discrimination and the analysis of proximity.

A major theory of early visual processing has recently been proposed by Marr, which considers a number of aspects of visual perception in great detail, including grouping and texture discrimination. New phenomena associated with texture discrimination are described and experiments reported which allow a preliminary comparison of Marr's theory, as it applies to texture discrimination, with more established theories such as that due to Julesz. One experiment produced results which are clearly consistent with Marr's account, but the ability of his theory to deal with additional data on region suppression is not established. The theory of the analysis of proximity relations proposed by Fox offers a broadly satisfactory account of many texture perception results, while relying on the more fundamental parts of Marr's theory of primitive visual processes to deal with the remainder. A further attraction of proximity analysis is that it may shed new light on the classical paradox of symmetry perception. Some ways in which the preliminary proximity analysis model is incomplete are discussed, and it is concluded that development of the model may be profitable for theories of early visual processing.

Discrimination, Psychological↗
PubMed2000

Multiple perceptual distortions and their modulation in leftsided visual neglect.

There is an ongoing debate concerning the perception and neural representation of space in neglect. Four experiments are here reported designed to further investigate the nature of perceptual distortions and their modifiability in patients with neglect. In Experiment 1 it was found that neglect patients, in contrast to left- or right-hemisphere lesioned control patients and normal subjects, show similar distortions of perceived visual space when judging the extension of horizontal distances (space distortion) as compared to the horizontal size of objects (size distortion). Similar deficits were present in most neglect patients in a newly developed space bisection task. These results attest that neglect patients have perceptual distortions related to within-object (size) and between-object (distance) spatial processing in their horizontal plane. Objects were oversized by 33% and distances by 19% horizontally in neglect patients, whereas all control groups showed nearly veridical spatial coding (deviations<5%). In Experiment 2 the modifiability of these distortions was tested by the use of slow visual background motion. Leftward, coherent background motion transiently restored normal horizontal size and distance coding in neglect patients, whereas rightward motion aggravated the deficit significantly in the distance task, but not in the size task. None of the other subject groups showed any influence of background motion on spatial judgments. Experiment 3 evaluated possible effects of simultaneous vs successive stimulus presentation in perceptual distortions, thus modulating attentional factors. Neglect patients performed significantly better - although not normal - with a successive presentation of the spatial stimuli (2 s, 10 s delay) as compared to the simultaneous condition in the size judgment task, but not in the distance task. In contrast, this manipulation had no effects in any of the control groups. Experiment 4 reports more detailed results of subject J.S., a neglect patient with a right mediotemporal lesion, who showed a marked horizontal size distortion, but normal horizontal distance judgments. Despite some fluctuation in J.S.'s size judgments he showed a significant overestimation of horizontal object size by +22% to +40% across several test blocks and testing sessions. Thus, performance fluctuations due to attentional or other reasons cannot fully account for J.S.'s dissociation in size vs distance judgments. He thus shows that the visual coding of horizontal spatial extension within an object can be dissociated from that of the spatial extension between objects along the horizontal plane. Finally, performance in the three spatial tasks (used in Experiment 1) was found to correlate significantly with three typical tests of spatial neglect (line bisection, cancellation, copying, r=0.42-0.77), thereby indicating a significant relationship to the neglect syndrome.Together, the results of the four experiments are interpreted in support of multiple spatial-perceptual distortions in visual neglect, which are influenced by visual motion and attention. Perceptual distortions relating to objects and space between objects are present in most neglect patients, but may dissociate, as in case J.S. It is argued that these might reflect the existence of several, partially overlapping and diverging neural maps for the representation of different spatial attributes in the horizontal plane. Furthermore, it is hypothesized that these perceptual distortions constitute an important element of the spatial-perceptual deficits encountered in the syndrome, contribute to its severity, but are not the key deficit of the disorder.

Aged↗
PubMed2000

Drivers' impressions of front and rear gaps in queues.

Drivers' opinions on, and perception of, gaps to a leading and a following car were studied in two field experiments. In study 1, the drivers indicated their opinion on adequate, critical and legal gap to a leading and a following car at 40 and 80 km/h. The results showed that drivers indicated longer front gaps than rear gaps in all conditions. In study 2, the drivers made judgements of distance to a leading and a following car when standing still and when travelling at 80 km/h. They were also asked to manoeuvre to a position in the middle between the leader and the follower. The results in study 2 revealed a perceptual bias in the driver when travelling at 80 km/h in that the drivers were closer to the follower when they thought they were in the middle between the leader and the follower. Gaps were generally underestimated and front gap was more underestimated than rear gap. The differences between opinions on gaps in the forward and the rearward directions could, partly, be explained by a perceptual bias in the driver. The bias should have a safety-promoting effect since it makes the driver more tolerant against short rear gaps than without the bias.

Adult↗
PubMed1994

[Standardized analysis of visuospatial perception. Studies of objectivity, reliability and validity].

Retest reliability and validity of a computational method (VS, [19]) for the analysis of visual spatial perception in brain damaged patients was investigated. Retest reliability was tested in 20 patients (retest interval: 1 week; range: 1-3) and varied from r = 0.65-0.95 for the different subtests for the "point of subjective equality" and r = 0.39-0.89 for the "interval of uncertainty". In the several investigations concerning the validity of VS. 234 patients and 10 normal subjects participated. In the first place, we found significant relationships of some of the subtests of VS to similar visual-spatial tests, but no relationship to tests of visual object perception. Secondly, we found significant relationships to certain tasks which approximated daily functioning. In summary, the present results demonstrate the objectivity, retest-reliability and validity of VS in brain damaged patients.

Adolescent↗
PubMedDate not supplied

The gap in your knowledge: gender on wheels.

Among a group of young car drivers the size of the gap perceived as necessary to allow them to drive their cars through was related to their degree of measured fatness. This relationship extended to measured height and shoulder breadth in women and self-perception of shoulder breadth in men. No relationship could be found with the premenstrual phase in women. These findings may have important social implications.

Adolescent↗
PubMed1977

Dynamic properties of radial and tangential movements as determinants of the haptic horizontal--vertical illusion with an L figure.

In four experiments involving blindfolded subjects, constant errors in the haptic judgment of extent in the horizontal plane were found to relate consistently to the time and velocity of limb movement. Radial movements, executed at a slower speed and for a longer time, are judged longer than tangential movements of equal extent. The data were considered in relation to certain physiological and kinematic properties of the actively moving limb. Taken together with additional information on judgments of movement duration, the results suggest that the illusion of extent is modulated by the perception of differential time cues. In these terms, it was noted that the haptic horizontal-vertical illusion with the L figure is another instance of the interaction of apparent space and time commonly found in studies of psychological relativity.

Adolescent↗
PubMed1999

Objects of attention, objects of perception.

Four experiments were conducted, to explore the notion of objects in perception. Taking as a starting point the effects of display content on rapid attention transfer and manipulating curvature, closure, and processing time, a link between objects of attention and objects of perception is proposed. In Experiment 1, a number of parallel, equally spaced, straight lines facilitated attention transfer along the lines, relative to transfer across the lines. In Experiment 2, with curved, closed-contour shapes, no "same-object" facilitation was observed. However, when a longer time interval was provided, in Experiment 3, a same-object advantage started to emerge. In Experiment 4, using the same curved shapes but in a non-speeded distance estimation task, a strong effect of objects was observed. It is argued that attention transfer is facilitated by line tracing but that line tracing is encouraged by objects.

Adult↗
PubMed1976

Field dependency and perceptual cues in perception of two trapezoid illusions.

40 males and 40 females rated as field-independent or field-dependent on the Group Embedded-figures Test were tested on two dynamic trapezoid illusions and made position judgments of static trapezoidal targets. Field-independent subjects reported more illusory experiences on the perception of rotation of an oscillating target than the perception of oscillation of a rotating target. The opposite was true for field-dependent subjects. Position judgments were related to the latter illusion but not the former. There was strong evidence of a differential use of perceptual cues for the two dependent groups.

Adolescent↗
PubMed2003

A common perceptual parameter for stair climbing for children, young and old adults.

In this paper we examine whether a common perceptual parameter is available for guiding old adults, young adults and children in climbing the highest stair mountable in a bipedal fashion. Previous works have shown that the ratio between the height of the stair and the hip height was the body-scaled invariance adopted as information for selecting the highest stair by young adults [Journal of Experimental Psychology: Human Perception and Performance 10 (1984) 683-703] but not by older adults [Journal of Experimental Psychology: Human Perception and Performance 3 (1992) 691-697]. Indeed, for older adults additional bio-mechanical parameters needed to be added to the model due to their decrease in leg strength and flexibility.Up to now, no perceptual invariant has been identified yet for determining the relevant information used for guiding the stair climbing action for normal healthy people. We propose a new parameter as the angle defined by the ratio between the height of the stair and the distance taken from the feet to the top edge of the stair before the initiation of the movement. We show that this angle is the same for children, young adults and older adults despite the different kinematics of the motion, the anthropometrics and the skill ability exhibit by the participants. In summary we show that even when the climbability judgments, based on the simple ratio leg length-stair height, are influenced by differences in age, participants use a common perceptual variable when they are coordinating their stair climbing action.

Adult↗
PubMed1977

Mathematical model for assimilation and contrast in perception of extent.

A mathematical model for assimilation and contrast in the perception of extent is presented, and predictions generated from the model are empirically tested. Implications of the model for the Müller-Lyer illusion are dealt with explicitly, and implications of the model for the Delboeuf, Ebbinghaus, and other illusions of extent are discussed in general terms.

Discrimination, Psychological↗
PubMed1967

Human echo perception.

It has been shown that human test subjects have the ability, under controlled laboratory conditions, to use echoes to detect the presence or absence of targets placed before them. In addition, blind and sighted persons have been able to detect a target monaurally, to make simple shape discriminations, and to locate a target in space. Signal, environmental, and individual variability affect performance in a measurable fashion. This research is an initial step in measuring the limits of a human being's ability to use echoes as a source of information about his physical surroundings. At this point it seems unlikely that the unaided human ear can rival the bat's auditory system for echo perception. It may be, however, that modern technology can partially bridge the evolutionary gap and bring more useful echoes to man's ear than those it now receives. Such an accomplishment would allow us to examine the extent to which man might benefit from this means of sensing his environment.

Distance Perception↗
PubMed1977

Effect of weight and sex on perception of line length.

56 obese and 103 normal-weight college students were asked to make line-length estimations of lines on either a light or dark background. Analysis of the results showed significant interactions between weight and contrast and sex and contrast, with the line estimations by women and normal weight individuals being more dependent on the contrast.

Body Weight↗
PubMed1999

Assimilation and contrast in geometrical illusions: a theoretical analysis.

It is argued that an unwarranted dichotomization of geometrical illusions has produced theories whose explanatory scope is limited to either assimilation or contrast. Since recent attempts at integration lack precision, a 1977 unified model of the perception of extent by Brigner was revised to predict accurately both assimilative and contrastive phases of the parallel lines illusion. Application of the revised model to other geometrical illusions was discussed and a means of parsimoniously accounting for variations in assimilative illusions occurring with age and with lightness of the stimulus figure was suggested.

Age Factors↗
PubMed1993

[Standardized analysis of visual spatial perception. Construction of the procedure and applications].

Assessment of visuo-spatial perception (VS) in brain-damaged patients. So far, no comprehensive methods for reliable assessment of visuo-spatial deficits after brain damage have been described. The tests usually applied are subtests of intelligence tests, paper-pencil tests or visual-constructive tests which also require motor and planning abilities. Almost all these methods are unsuitable for measuring therapeutic changes and do not reveal specific impairments. The computational method presented here (VS) is suitable for the quantitative assessment of visuo-spatial functions, e.g. subjective visual vertical and horizontal; orientation, length, distance, form and position discrimination as well as line bisection. It can easily be installed on an IBM compatible PC. A clinical standard examination can be performed within 20-30 minutes including numerical and graphical analysis of the results. The method is sensitive for measuring therapeutic changes. Moreover, it offers a wide range of experimental task manipulations for more sophisticated experimental tests.

Attention↗
PubMed1997

Correcting some misperceptions of time-to-collision: a critical note.

Stewart et al (1993, Perception 22 1227-1224) attempted to demonstrate that the ratio of angular speed to angular acceleration, [symbol see text]/[symbol see text], of the approaching object is preferred as the source of time-to-collision information to the ratio of visual angle to angular speed, [symbol see text]/[symbol see text]. It is demonstrated that this is not justified.

Distance Perception↗
PubMed1991

General practitioners' perceptions of the effects of a distance learning programme.

A postal/telephone survey of 400 general dental practitioners working in the Greater Glasgow and Lanarkshire Health Board areas was carried out between May and September 1990. The aims were to monitor any changes in the use of sealant restoration techniques in the last year, to investigate the practitioners' perception of the effects of a distance learning programme on their techniques and to provide data on the use of the techniques in the final months of the 'old contract'. A response rate of 66.7% was achieved. Eighty-eight per cent of the group were placing sealant restorations. Dentists' perceptions of the impact of the distance learning programme were encouraging. In key areas of practice, 16-44% of the group reported changes in their clinical techniques as a result of reading the programme.

Dental Fissures↗
PubMed1999

Haptic perception of linear extent.

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.

Adolescent↗
PubMed1999

Perceiving the sweet spot.

Many sports involve aligning a hitting implement with a ball trajectory such that contact is made at the implement's center of percussion or 'sweet spot'. This spot is not visibly distinct; its perception must be haptic. Although it is functionally defined with respect to contact--it is the point of impact that produces the least vibration in the hand holding the implement--hitting success requires appreciating the location of the sweet spot prior to contact. Two experiments verified that perceivers (novices as well as expert tennis players) distinguished perception of length from perception of the position of the sweet spot simply on the basis of wielding, both for tennis rackets and for bats contrived from wooden rods with attached masses. Results conformed to previous research on dynamic touch in showing that perceiving the lengths of wielded objects, including selectively perceiving partial lengths, is constrained by inertial properties of the object.

Adult↗