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PubMed1993

Open trial of subjective precision tinting: a follow-up of 55 patients.

We gave glasses, tinted using new techniques, to 55 patients with visual discomfort and a range of associated complaints. The techniques permitted the patients to adjust the colour and saturation of tint for maximum clarity and comfort when viewing text. Benefit was experienced by 45 patients (82%) who were still using them more than 10 months later. Of these, 40 presented with a perceptual distortion of text that the glasses alleviated; 86% reported migraine in the family. An independent series of 74 children with reading difficulty was examined using coloured plastic sheets placed upon a page of text. Of those reporting beneficial effects of colour, 60% had migraine in the family, as compared with 31% of those for whom colour was of no benefit.

Adolescent↗
PubMed2001

Categorical perception of face identity in noise isolates configural processing.

Neuropsychological evidence suggests that face recognition based on configural (holistic) information can occur in isolation from recognition based on local feature cues. The present study shows that configural processing can be isolated experimentally in normal subjects. A phenomenon is reported that exists only for upright whole faces, namely categorical perception (CP) of face identity in noise. Three discrimination tasks (ABX, better likeness, and similarity ratings) were used to test for perceptual distortion across the category boundary predicted from binary classification of face morphs. Noise was added such that any single local region provided unreliable cues to identity. Under these conditions, CP was found for upright faces but not for inverted faces or single features, even with more than 10,000 trials. The CP-in-noise signature phenomenon was then used to show that configural processing survives image plane rotations of 45 degrees-90 degrees.

Adult↗
PubMed1994

Mueller-Lyer illusion and size estimation performance in schizophrenics compared to normal controls.

A size estimation (SE) paradigm and the Mueller-Lyer (ML) illusion were used to examine perceptual disturbances in schizophrenics. 35 reliably diagnosed (DSM III-R) schizophrenics were compared to 20 subjects with no history of psychiatric illness. Perceptual distortions found in previous studies of schizophrenics were only to a certain extent confirmed in the present results. More overestimators were found among the schizophrenics than among the normals on the SE task. The schizophrenics, first of all the chronic patients, also proved to be more prone to the Mueller-Lyer illusion. A reason why the very clear differences between schizophrenics and normals found in previous examinations were not confirmed in the present study, might be that a reliable diagnostic instrument was for the first time used in this kind of study.

Adult↗
PubMed2002

Dissociation between location and shape in visual space.

There are often large perceptual distortions of shapes lying on the ground plane, even in well-lit environments. These distortions occur under conditions for which the perception of location i saccurate. Four hypotheses are considered for reconciling these seemingly paradoxical results, after which 2 experiments are reported that lend further support to 1 of them--that perception of shapeand perception of location are sometimes dissociable. The 2 experiments show that whereas perception of location does not depend on whether viewing is monocular or binocular (when other distance cues are abundant), perception of shape becomes more veridical when viewing is binocular. This means that perception of shape is not fully constrained by the perceived locations of the vertices that define the shape.

Adolescent↗
PubMed1999

Dynamic capture of sound motion by light stimuli moving in three-dimensional space.

A moving light stimulus produced a sensation of motion for a stationary sound stimulus presented simultaneously, which was called the dynamic visual capture by Mateeff, Hohnsbein, and Noack in 1985. The present study examined whether the moving light stimulus might induce a perceptual shift in the velocity, that is, the speed and the direction, of a moving sound stimulus. This type of the visual capture was explored in the directions where the sound stimulus moved along the motion tracks of the light stimulus: first in a horizontal and a vertical orientation and secondly in a depth orientation. Moreover, perceptual distortion of the direction of movement of the sound stimulus was investigated when the direction from which a sound stimulus moved deviated from the motion tracks of a light stimulus. It was found that the dynamic visual capture was inducible in all of three orientations, appearing more strongly in the vertical and the depth orientations than in the horizontal orientation. The perceived direction of the moving sound stimulus was greatly influenced by the direction where the light stimulus moved simultaneously and was often the same as the physical direction of the light stimulus, even when the physical motion directions of those two stimuli were perpendicular or opposite each other.

Acoustic Stimulation↗
PubMed1999

Starting position of movement and perception of angle of trunk flexion while standing with eyes closed.

The present study attempted to investigate the effect of position on the perception of angle of trunk flexion while standing. For this purpose, the range effect was factored out by setting the constant target angle at 10 degrees, with varied starting positions of trunk flexion. We found that subjects underestimated angle of trunk flexion when the starting position was close to a quiet standing posture, overestimated when close to maximum trunk flexion, and correctly perceived it when at the middle position. Less perceptual distortion was observed at the positions close to maximum trunk flexion in the present study than in our previous one, in which various target angles of trunk flexion were reproduced from a quiet standing posture. The reduced distortion in the present study was believed to have resulted from factoring out the range effect. The flexion angle of the hip joint changed in tandem with that of the trunk, while very little movement was observed in the ankle, knee, and neck joints. Judging from the changing pattern of hip-joint angle, the muscle activity of the erector spinae and biceps femoris increased gradually to 90 degrees trunk flexion. In contrast, the actual increment of muscle activity reached zero or a minimum value at the middle angles as the angle of trunk flexion increased. It was assumed that the abrupt change in kinesthetic information associated with muscle activity exerted a great influence on the perception of trunk flexion.

Hip Joint↗
PubMed1996

Amblyopic quasi-blindness for image structure.

Human amblyopes display reduced contrast sensitivities, suffer from perceptual distortion, and their letter acuities are worse than is predicted from grating visibility. We sought the origin of these dysfunctions by measuring normal and amblyopic sensitivities to various forms of well-defined image distortion, namely band-limited phase quantization, phase quantization with additional amplitude modulation, and grey-scale modification. Our results prove the existence of an amblyopic quasi-blindness to image structure, that cannot be explained in terms of contrast detection. We discuss these findings within the computational scheme of image decomposition into local amplitude and local phase values. they are consistent with the assumption of amblyopic eyes beings impaired in processing local phase but having the local amplitude (or "energy", possibly at reduced gain) at their disposal. Phrased in physiological terms, we propose a scheme of complex-cells-only vision in amblyopia. We also provide a demonstration of how amblyopic eyes may see the test stimuli and natural images by generating local amplitude and phase representations at limited phase resolution.

Amblyopia↗
PubMed1992

Percept-genetic signs of repression in histrionic personality disorder.

Several types of perceptual distortions of two anxiety-arousing visual stimuli are coded as repression in the Defense Mechanism Test, a tachistoscopic, percept-genetic technique. Given the well-established correspondence between hysteria and repression, the study included a clinical validation of these variants of repression against the diagnosis of histrionic personality disorder. 41 subjects with evidence of this disorder on the Millon Clinical Multiaxial Inventory-II were compared with 41 nonhistrionic controls. Significantly more histrionics were coded for the type of repression in which the threatening figure is transformed into a harmless object (code 1:42), while animal- and statue-repressions, when combined (codes 1:1 and 1:2), were significantly more characteristic of the nonhistrionic group. As an unpredicted finding, significantly more histrionic subjects employed defensive strategies, currently coded as reaction formations (code 4:). Histrionic subjects without concomitant compulsive features were coded more frequently for introaggression (code 6:) compared both with nonhistrionic controls and with histrionic-compulsive subjects. The findings are discussed within the context of the available percept-genetic literature. It is suggested that the Defense Mechanism Test may be further employed to objectify and investigate the defense mechanisms of the DSM-III-R disorders.

Adult↗
PubMed1994

Angular induction as a function of the length and position of segments and gaps.

The perceptual distortions which are manifested in the Poggendorff illusion can be studied with the use of a more restricted set of stimulus elements. Experiments were designed in which angular induction effects between two line elements, known respectively as the test segment and induction segment, were evaluated. In some stimulus configurations the induction 'segment' consisted of a tandem pair of segments. Previous studies had shown that the induction segment will bias operant judgments of collinearity for a test segment, this effect being a function of the relative angle between the two. Six experiments are reported, in which the length and position of segments in relation to the tip of the test segment were varied. It was found that substantial induction is produced by a very short segment, and that this can bias judgment even when its displacement spans more than 10 deg of visual angle. Several aspects of the data suggest that the strength of effect is a log-linear function of segment position. However, the results from displacement of single or tandem segments do not conform to predictions based on length/response summation, and thus do not support a linear-systems approach. Neural substrates for these interactions are given brief attention.

Adult↗
PubMed1995

Optometric correlates of Meares-Irlen syndrome: a matched group study.

People who report visual perceptual distortions, typically when reading, that are alleviated by using coloured filters are described as suffering from 'Meares-Irlen Syndrome'. A recent double-masked placebo-controlled trial showed that this condition cannot be solely explained as a placebo effect and that the beneficial filter is idiosyncratic and sometimes needs to be highly specific. Several mechanisms have been suggested for Meares-Irlen Syndrome including ocular motor (binocular and accommodative) anomalies, a sensitivity to patterned stimuli (pattern glare), and a deficit of the transient visual sub-system. We investigated these hypotheses by comparing 16 children, who reported the symptoms described above and who showed a sustained benefit from coloured filters, with 25 control children who came from the same school and were matched for age, reading performance and intelligence. The 'Meares-Irlen Syndrome' group had slightly, but significantly, reduced vergence and accommodative amplitudes and stereo-acuity; they also demonstrated significantly more pattern glare. The two groups did not differ significantly in their visual acuities, refractive error, dissociated or associated heterophoria, AC/A ratio, or ability to perceive 20 Hz flicker. It appears that certain ocular motor factors are correlates of Meares-Irlen Syndrome, rather than the primary underlying cause of the symptoms. The results support the hypothesis that pattern glare may be involved in the mechanism of Meares-Irlen Syndrome.

Accommodation, Ocular↗
PubMed2005

Increasing reading speed by using colours: issues concerning reliability and specificity, and their theoretical and practical implications.

By using techniques for precision ophthalmic tinting, individuals who report perceptual distortion of text can often find a colour of illumination that eliminates the distortions and increases reading speed. Most individuals choose green or blue hues, but there is considerable variability. We investigated how specific the colour has to be to obtain optimal reading speed. Individuals who habitually wear coloured filters for reading were asked to read text illuminated by coloured light (without using their filters). Reading speed was measured repeatedly with light of different colours. The colour (chromaticity) at which reading was fastest was consistent from one test session to the next. It was different from one individual to another, but highly specific for each individual: departures of colour from optimum by about 6 JNDs eliminated most of the speed advantage conferred by the optimal colour. It was difficult to attribute the consistency and specificity simply to familiarity with the tint or immediate memory for the colour of illumination. A consecutive sample of 1000 tint prescriptions was analysed numerically. For most prescriptions the variation in chromaticity with different types of lighting was not such as to remove all the potential benefit of the tint, as judged from a model of the effect of chromaticity on reading speed. The exceptions were the few tints that were weakly saturated or purple in colour. Across participants, reading speed was not consistently related to the scotopic energy, to the energy captured by any cone class, or to opponent colour processes. The reading was generally slowest with white light, and not with the colour complementary to the optimum. Explanations in terms of magnocellular deficits and cortical hyperexcitability are briefly discussed.

Adolescent↗
PubMed1996

Semantic and visual factors affecting the representation of map information.

In past research evidence has been found for both mental imagery and propositional hierarchies in subjects' map representations. How the visual and semantic factors associated with maps influence the use of one form of representation or another was the subject of the study reported here. Subjects were required to make relational judgments about city pairs. The results of experiment 1 indicated that superordinate relationships (the relationship of the counties of which the cities were members) affected only the most difficult perceptual judgments, but affected all judgments made from memory. Experiment 2 was done to determine the extent to which these findings were attributable to perceptual distortions rather than propositionally stored rules. Results of experiment 3 showed the degree of perceptual distinction necessary for propositional rules to have no significant influence on relational judgments.

Analysis of Variance↗
PubMed1983

Assessment of perceptual discrepancy: utility of the Primary Communication Inventory.

The Primary Communication Inventory was factor-analyzed in order to validate the subscales of this instrument. These subscales were derived by Navran (20) on the basis of face validity and were labeled verbal and nonverbal communication subscales. The analysis yielded two factors. However, they could not be labeled verbal and nonverbal. Instead, the factors were interpreted as: (a) the individual's perceptions of own communication ability, and (b) the spouse's perceptions of the individual's communication ability. The scoring of the Primary Communication Inventory was revised and used as a measure of perceptual discrepancy between husbands and wives. Interestingly, discrepancy within the marital dyad was greater for the nondistressed participants than for the distressed participants. The results illustrate the potentially adaptive nature of positive perceptual distortion within the marital dyad and the potential utility for future research of calculating perceptual discrepancy scores for each spouse using the Primary Communication Inventory.

Adult↗
PubMed1998

Visual size processing in spatial neglect.

Evidence from the use of the landmark task and from two size-matching tasks shows that many patients with left-sided neglect systematically under-perceive visual extent in leftward parts of space. This perceptual distortion of size serves to explain the occurrence of rightward line-bisection errors in most neglect patients. One possibility is that attentional biases of a chronic nature might underlie these perceptual changes seen in neglect patients. But contrary to this idea, we have found that attentional cueing in the landmark task causes changes in neglect patients exactly opposite to those seen in healthy subjects. The distortions of size perception seen in neglect could instead be caused by a high-level alteration of visual processing rather than by an attentional bias. In order to explore which visual stream of cortical processing might be compromised in such a disorder, we have begun to examine neglect patients on visuomotor as well as perceptual tasks. We have found clear evidence in one patient for intact grip scaling for object size in the neglected half of space, despite gross perceptual underestimations of the same objects. This result suggests that neglect can occur without major disruption of the dorsal stream, and may result instead from damage to a cortical system whose predominant visual input comes from the ventral stream.

Attention↗
PubMed1994

Visual processing, lateralization and syndromes of schizotypy.

There is an association between positive features of schizotypy and dyslexia, largely involving distortions of visual and auditory perception and associated cognitive anomalies. In dyslexia, there is strong evidence for a disorder of subcortical magnocellular pathways, which may underlie these perceptual aberrations. Here we investigated visual processing in relation to three syndromes of schizotypy-Active, Withdrawn and Unreality-in normal adults, using a "dot localization" test of visual direction sense on which dyslexics perform poorly, and which should be sensitive to magnocellular dysfunction. Results showed that increased error scores were associated with both the positive syndromes, Active and Unreality, which in this study were highly correlated. There were also interactions between each syndrome and the direction of errors, such that high scorers on the Unreality and Active syndromes made more errors on leftward trials, while high Withdrawn subjects made fewer left and more right errors. Mixed handers also showed poorer performance than consistent handers. The evidence of poor visual direction sense in relation to positive syndromes of schizotypy and mixed handedness is consistent with the previous results for dyslexics, who also show these features. The opposite lateralization of errors in the positive v negative syndromes of schizotypy is in keeping with the model of hemisphere imbalance and patterns of cognitive asymmetry which distinguish Active from Withdrawn syndromes. These results are considered in relation to the proposal that a disorder of magnocellular function may underlie the perceptual distortions which are common to dyslexia and positive syndromes of schizotypy.

Adolescent↗
PubMed1996

The tilt aftereffect in plaids and gratings: channel codes, local signs and "patchwise" transforms.

The perceived structure of a suprathreshold plaid made from two sinusoidal gratings tilted +/- 45 deg from vertical usually resembles a blurred checkerboard. Physically increasing the tilt of the components away from vertical elongates the pattern horizontally, yielding rectangular checks. We asked whether illusory tilt of the components induced by adaptation to a vertical grating would also give apparent elongation of the checks. Using a staircase method, we found that after adaptation the component orientations had to be set 3-4 deg closer to vertical to maintain a square, checkerboard-like appearance, implying that the +/- 45 deg plaid did appear elongated. This result suggests that the tilt aftereffect adaptation not only distorts the orientation of 1-D patterns but can also change the relative location of features, even when their orientation is not altered. This is not easy to explain within filter models that (often implicitly) assume each receptive field carries a fixed "local sign" indicating its position within the retinal array. We consider a representation in which localized patches of the image are encoded by the coefficients of a 2-D Fourier-like transform. With a simple subtractive model of adaptation, we show that the spatial information carried by each patch would be distorted in just the way observed for plaids and gratings. The fact that perceived structure is both distorted and coherent, not fragmented, after adaptation suggests an additional, more global process whereby local patches are combined to form a coherent, composite "neural image". We offer a simple principle that could establish this coherence. If the positions of local patches are adjusted so as to maximize the contrast energy of the composite image, then the spatial distortions of the patches (induced by selective adaptation) are carried through to the global structure of the composite. Thus, the conflict between channel codes and local signs is resolved, but perceptual distortion is the result.

Adaptation, Ocular↗
PubMed1997

Abnormal long-range spatial interactions in amblyopia.

Neural interactions between widely separated stimuli were explored with psychophysical and visual evoked potential (VEP) measures in normal and amblyopic observers. Contrast detection thresholds were measured psychophysically for small foveally viewed Gabor patches presented in isolation and in the presence of similar, but laterally displaced flanks. The amplitude and phase of VEPs elicited by similar targets were also measured. The presence of neural interaction between the target and flank responses was assessed by comparing the unflanked threshold to the flanked threshold in the psychophysical experiments and by comparing the response predicted by the algebraic sum of test and flank responses to that measured when test and flanks were presented simultaneously. In normal observers simultaneous presentation of test and flank targets produces a VEP response that is up to a factor of two larger than the linear prediction (facilitation). Psychophysical threshold is also facilitated by a comparable factor. Facilitation was found mainly for configurations in which local (carrier) and global (patch) orientations resulted in collinearity, independent of global orientation (meridian). Amblyopic observers showed several deviations from the normal pattern. The facilitation for the collinear configurations was either markedly lower than normal or was replaced by inhibition. The normal pattern of spatial interaction may facilitate the grouping of collinear line segments into smooth curves. In contrast, abnormal long-range spatial interactions may underlie the grouping disorders and perceptual distortions found in amblyopia.

Amblyopia↗
PubMed1981

Position cues in discrimination behaviour of normal, Down syndrome and other mentally handicapped children.

Groups comprising twelve Down syndrome, twelve other mentally handicapped children and twelve normal children, matched for M.A., were tested on a visual discrimination task. There was some evidence to support the suggestion that certain types of mentally handicapped children attended to single cues, rather than to total configuration. There was also evidence of perceptual distortion resulting in reversal and attraction to "good form". Differences were detected between Down syndrome and non-Down syndrome handicapped children which were consistent with the suggestion that Down syndrome children characteristically show flexibility in approach to perceptual discrimination tasks. The results were not inconsistent with interpreting perceptual processes in handicapped and normal children as essentially similar.

Child↗