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PubMed1998

Blindsight and shape perception: deficit of visual consciousness or of visual function?

Two people with homonymous right hemianopias were tested on a number of measures of non-conscious and conscious perception of shape in the blind field. Experiment 1 examined preparatory manual adjustments in grasping objects. Both subjects performed well above chance not only in three-dimensional location but also in preforming the hand to the shape, size and orientation of objects. In Experiment 2 single upper-case letters were briefly exposed in the blind field, and subjects made forced choices among 6 alternatives in the sighted field. Performance improved over blocks of trials and was above chance, but not dramatically. In Experiment 3 single upper-case words were briefly presented in the blind field, and subjects chose which of two words exposed after in the intact field was semantically closer. In Experiment 4 subjects had to give the meaning of single ambiguous words (e.g. BANK) presented both visually in the intact field and auditorily. Each ambiguous word was preceded by a single upper-case word briefly presented in the blind field, biasing each meaning on different blocks of trials (e.g. MONEY and RIVER). In Experiment 3, although results were in the appropriate direction, they were not consistently well above chance. By contrast, in Experiment 4 both subjects were consistently semantically biased to a high degree by words in the blind field. Experiments 2, 3 and 4 taken together suggest that indirect techniques (priming) are more sensitive to showing effects of non-conscious perception than direct ones (forced-choice). More importantly the experiments indicate that not only orientation but curvature, structural descriptions of component strokes and spatial ordering of letters are registered non-consciously in the blind field. Experiment 5 examined after-images in the blind and sighted fields, showing veridical conscious perception of shape in the blind field provided it was accompanied by a shape in the sighted field which together formed a good Gestalt. Experiment 6 showed conscious perception of illusory contours spanning the hemifields induced by Kanizsa figures. The experiments suggest that aspects of shape are much better perceived in blindsight than previously thought, that this is independent of their use in motor control, that the main deficit in blindsight is one of consciousness, and that the loss of conscious vision in the blind field is far from total. The effects and their relationship to those in other neuropsychological deficits suggest an intimate link between perceptual consciousness, attention and object perception.

Afterimage↗

PubMed2005

Differential involvement of the cerebellum in biological and coherent motion perception.

Perception of biological motion (BM) is a fundamental property of the human visual system. It is as yet unclear which role the cerebellum plays with respect to the perceptual analysis of BM represented as point-light displays. Imaging studies investigating BM perception revealed inconsistent results concerning cerebellar contribution. The present study aimed to explore the role of the cerebellum in the perception of BM by testing the performance of BM perception in patients suffering from circumscribed cerebellar lesions and comparing their performance with an age-matched control group. Perceptual performance was investigated in an experimental task testing the threshold to detect BM masked by scrambled motion and a control task testing the detection of motion direction of coherent motion masked by random noise. Results show clear evidence for a differential contribution of the cerebellum to the perceptual analysis of coherent motion compared with BM. Whereas the ability to detect BM masked by scrambled motion was unaffected in the patient group, their ability to discriminate the direction of coherent motion in random noise was substantially affected. We conclude that intact cerebellar function is not a prerequisite for a preserved ability to detect BM. Because the dorsal motion pathway as well as the ventral form pathway contribute to the visual perception of BM, the question of whether cerebellar dysfunction affecting the dorsal pathway is compensated for by the unaffected ventral pathway or whether perceptual analysis of BM is performed completely without cerebellar contribution remains to be determined.

Adult↗

PubMed1989

Pupils' perceptions of school and teachers. I--Identifying the underlying dimensions.

Previous comparative studies have shown interesting differences in motivation and approaches to learning between Britain and Hungary, which were considered to reflect different methods of teaching. The present study reports the development of scales designed to measure pupils' perceptions of school and teachers with the intention of relating those perceptions to school motivation and approaches to learning. The scales covered a wide range of aspects relating both to pupils' perceptions of school ethos and aspects of the learning environment. An inventory made up of 18 five-item Likert scales describing perceptions of school and teacher was given to samples of 516 12-15 year-old pupils in five British schools and a comparable sample of 602 pupils in Hungary. The factor structure of the school and teacher perceptions scales was almost identical in the two countries, suggesting that pupils perceive their schools in very similar ways in spite of the contrasting educational and social systems. There were differences between schools which, although small at the scale level, were sometimes large at the level of individual items. It is suggested that a revised set of scales which have been derived from these analyses might be used by schools to judge the way they are perceived by their pupils, and so also by the parents who will be having more influence in future on school policy and management.

Adolescent↗

PubMed2006

Auditory-visual speech perception and synchrony detection for speech and nonspeech signals.

Previous research has identified a "synchrony window" of several hundred milliseconds over which auditory-visual (AV) asynchronies are not reliably perceived. Individual variability in the size of this AV synchrony window has been linked with variability in AV speech perception measures, but it was not clear whether AV speech perception measures are related to synchrony detection for speech only or for both speech and nonspeech signals. An experiment was conducted to investigate the relationship between measures of AV speech perception and AV synchrony detection for speech and nonspeech signals. Variability in AV synchrony detection for both speech and nonspeech signals was found to be related to variability in measures of auditory-only (A-only) and AV speech perception, suggesting that temporal processing for both speech and nonspeech signals must be taken into account in explaining variability in A-only and multisensory speech perception.

Acoustic Stimulation↗

PubMed2005

Chromatic perceptive field sizes change with retinal illuminance.

The effect of retinal illuminance (0.3-3.3 log td) on chromatic perceptive field size was investigated at 10 degrees eccentricity along the horizontal meridian of the temporal retina. Using the 4+1 color-naming procedure, observers described the hue and saturation of a series of monochromatic stimuli (440-660 nm, in 10-nm steps) of various test sizes (.098-5 degrees) after 30-min dark adaptation. Perceptive field sizes of the four elemental hues and the saturation component were estimated for each wavelength at each retinal illuminance. Results indicate that perceptive field sizes for blue, green, yellow, and saturation all decrease with increasing retinal illuminance; the perceptive field size for red is the smallest and invariant with intensity. The influence of rods on perceptive field size may account for some of the results; other factors are also considered.

Adult↗

PubMed2004

Integrative cortical dysfunction and pervasive motion perception deficit in fragile X syndrome.

BACKGROUND: Fragile X syndrome (FXS) is associated with neurologic deficits recently attributed to the magnocellular pathway of the lateral geniculate nucleus. OBJECTIVE: To test the hypotheses that FXS individuals 1) have a pervasive visual motion perception impairment affecting neocortical circuits in the parietal lobe and 2) have deficits in integrative neocortical mechanisms necessary for perception of complex stimuli. METHODS: Psychophysical tests of visual motion and form perception defined by either first-order (luminance) or second-order (texture) attributes were used to probe early and later occipito-temporal and occipito-parietal functioning. RESULTS: When compared to developmental- and age-matched controls, FXS individuals displayed severe impairments in first- and second-order motion perception. This deficit was accompanied by near normal perception for first-order form stimuli but not second-order form stimuli. CONCLUSIONS: Impaired visual motion processing for first- and second-order stimuli suggests that both early- and later-level neurologic function of the parietal lobe are affected in Fragile X syndrome (FXS). Furthermore, this deficit likely stems from abnormal input from the magnocellular compartment of the lateral geniculate nucleus. Impaired visual form and motion processing for complex visual stimuli with normal processing for simple (i.e., first-order) form stimuli suggests that FXS individuals have normal early form processing accompanied by a generalized impairment in neurologic mechanisms necessary for integrating all early visual input.

Adolescent↗

PubMed2004

Perceptibility curve test for conventional and colour-coded radiographs.

OBJECTIVE: A colour scale has been developed as a complement to the grey scale in radiographs. The aim of the present study was to compare colour-coded with conventional black-and-white radiographs in terms of the perceptibility curve test. MATERIALS AND METHODS: Twelve digital radiographs were exposed on a test object from low to high exposures and recorded using the DIXI system (Planmeca Oy, Helsinki, Finland). An aluminium test object was used containing ten object details in the form of holes with depths ranging from 0.03 mm to 0.30 mm in steps of 0.03+/-0.01 mm. The new colour scale was used to transform the conventional black-and-white radiographs into colour radiographs by specially designed software. Ten observers were asked to analyse four sets of radiographs, i.e. colour-coded and black-and-white radiographs, and reversed colour-coded and reversed black-and-white radiographs. The object detail having the lowest perceptible contrast in each radiograph was registered for each observer. Perceptibility curves were plotted based on the mean value of observer data. RESULTS: Results from the perceptibility curve test showed that the information in colour-coded radiographs was at least as good as that in black-and-white radiographs. In fact, in the lower exposure range, colour-coded radiographs exhibited better perception than conventional black-and-white radiographs. CONCLUSION: Radiographs that are colour-coded with the applied colour scale may be used as an alternative to conventional black-and-white radiographs.

Absorptiometry, Photon↗

PubMed2004

Time perception, impulsivity, emotionality, and personality in self-harming borderline personality disorder patients.

To investigate how time perception may contribute to the symptoms of self-harming Borderline Personality Disorder (BPD) patients, 19 self-harming BPD inpatients and 39 normal controls were given measures of time perception, impulsivity, personality, emotion, and BPD characteristics. A test sensitive to orbitofrontal cortex (OFC) function ("Frontal" Behavior Questionnaire) was also administered, as the OFC has been associated with impulsivity and time perception. BPD patients produced less time than controls, and this correlated with impulsiveness and other characteristics commonly associated with BPD. BPD patients were also less conscientious, extraverted, and open to experience, as well as more impulsive (self-report and behaviorally), emotional, neurotic, and reported more BPD characteristics, compared to controls. The results suggest that some of these core characteristics of BPD may be on a continuum with the normal population and, impulsivity in particular, may be related to time perception deficits (i.e., a faster subjective sense of time). Finally, BPD patients scored higher on the Frontal Behavior Questionnaire, suggesting that some symptoms of the BPD syndrome may be related to problems associated with the OFC. A control spatial working memory task (SWM) revealed that SWM deficits could not explain any of the BPD patients' poor performance. While impulsivity was correlated with time perception across all participants, emotionality, introversion, and lack of openness to experience were not. This suggests that different symptoms of the borderline personality syndrome may be separable, and therefore, related to different cognitive deficits, and potentially to different brain systems. This may have important implications for treatment strategies for BPD.

Adolescent↗

PubMedDate not supplied

Mechanisms of signal analysis and pattern perception in periodicity pitch.

Progress in the knowledge of auditory processing of complex sounds has been made through coordinated psychophysical, physiological and theoretical studies of periodicity pitch and combination tones. Periodicity pitch is the basis for human perception of musical notes and pitch of voiced speech. The mechanism of perception involves harmonic pattern recognition on the complex Fourier frequency spectra generated by auditory frequency analysis. Combination tones are perceptible distortion tones generated within the cochlea by nonlinear interaction of component stimulus tones. Perception of periodicity pitch is quantitatively accounted for by a two-stage process of frequency analysis subject to random errors and significant nonlinearities, followed by a pattern recognizer that operates very efficiently to measure the period of musical and speech sounds. The basic characteristic of the first stage is a Gaussian standard error function that quantifies the randomness in aural estimation of frequencies of component tones in a complex tone stimulus. Efficient aural measurement of neural spike intervals from the eighth nerve provides a physiological account for the psychophysical characteristic of aural frequency analysis with complex sounds. Although cochlear filtering is an essential stage in auditory frequency analysis, neural time following, rather than details of the filter characteristics, is the decisive factor in determining the precision of aural frequency measurement. It is likely that peripheral auditory coding is similar for sounds in periodicity pitch and in speech perception, although the 'second stage' representing central processing would differ.

Acoustic Stimulation↗

PubMed2005

Assessing the role of different spatial frequencies in word perception by good and poor readers.

Numerous studies indicate that dyslexic and nondyslexic individuals exhibit different patterns of sensitivity to spatial frequency. However, the extension of this effect to normal (nondyslexic) adults of good and poor reading abilities and the role played by different spatial frequencies in word perception have yet to be determined. In this study, using normal (nondyslexic) adults, we assessed reading ability, spatial frequency sensitivity, and perception of spatially filtered words and nonwords (using a two-alternative forced choice paradigm to avoid artifactual influences of nonperceptual guesswork). Good and poor readers showed different patterns of spatial frequency sensitivity. However, no differences in accuracy of word and nonword perception were found between good and poor readers, despite their differences in spatial frequency sensitivity. Indeed, both reading abilities showed the same superior perceptibility for spatially filtered words over nonwords across different spatial frequency bands. These findings indicate that spatial frequency sensitivity differences extend to normal (nondyslexic) adult readers and that a range of spatial frequencies can be used for word perception by good and poor readers. However, spatial frequency sensitivity may not accurately reveal an individual's ability to perceive words.

Humans↗

PubMed2006

The field dependence/independence cognitive style does not control the spatial perception of elevation.

Earlier work described the presence of a significant connection between an individual's ability to disregard distracting aspects of a visual field in the classical rod-and-frame test (RFT), in which a subject is required to set a rod so that it will appear vertical in the presence of a square frame that is roll tilted from vertical, and in paper-and-pencil tests, in which the subject is required to find a hidden figure embedded in a more complex figure (the Embedded Figures Test [EFT]; see, e.g., Witkin, Dyk, Faterson, Goodenough, & Karp, 1962; Witkin et al., 1954; Witkin, Oltman, Raskin, & Karp, 1971). This has led to a belief in the existence of a bipolar dimension of cognitive style that is utilized in such disembedding tasks--namely, the extent to which an individual is dependent on or independent from the influence of a distracting visual field. The influence of an inducing visual field on the perception of elevation measured by the setting of a visual target to appear at eye level (the visually perceived eye level [VPEL] discrimination) has also been found to be correlated with the RFT. We have thus explored the possible involvement of the dependence/independence cognitive style on the VPEL discrimination. Measurements were made on each of 18 subjects (9 of them female, 9 male) setting a small target to the VPEL in the presence of a pitched visual field across a range of six pitches from -30 degrees (topbackward) to +20 degrees (topforward) and on each of three tests generally recognized as tests of cognitive spatial abilities: the EFT, the Gestalt Completion Test, and the Snowy Pictures Test (SPT). Although there were significant pairwise correlations relating performance on the three cognitive tests (+.73, +.48, and +.71), the correlation of each of these three with the slope of the VPEL-versus-pitch function was not significant, as it was with the slope of the perception of visual pitch of the field (PVP)-versus-pitch function. VPEL, PVP, and a cognitive factor separated into three essentially independent factors in a multiple-factor analysis, with the three cognitive tests clustering at the cognitive factor, and with no significant loading on either of the other two factors. From the above considerations and a multiple-factor analytic treatment including additional results from this and other laboratories, we conclude that the cognitive-processing style held to be involved in the performance on the EFT and the perception of vertical as measured by the RFT is not general for egocentric space perception; it does not involve the perception of elevation.

Adolescent↗

PubMed2004

Effects of grouping and attention on the perception of causality.

Beyond perceiving patterns of motion in simple dynamic displays, we can also perceive higher level properties, such as causality, as when we see one object collide with another object. Although causality is a seemingly high-level property, its perception--like the perception of faces or speech--often appears to be automatic, irresistible, and driven by highly constrained and stimulus-driven rules. Here, in an exploration of such rules, we demonstrate that perceptual grouping and attention can influence the both perception of causality in ambiguous displays. We first report several types of grouping effects, based on connectedness, proximity, and common motion. We further suggest that such grouping effects are mediated by the allocation of attention, and we directly demonstrate that causal perception can be strengthened or attenuated on the basis of where observers are attending, independent of fixation. Like Michotte, we find that the perception of causality is mediated by strict visual rules. Beyond Michotte, we find that these rules operate not only over discrete objects, but also over perceptual groups, constrained by the allocation of attention.

Attention↗

PubMed1995

Does perceived size depend on perceived distance? An argument from extended haptic perception.

Two experiments were directed at the comparison between two perspectives on the perception of size achieved by probing the gap between two occluded distal surfaces by means of a hand-held rod. One perspective was the classical size-distance invariance hypothesis developed for the problem of visual size perception with a central role for perceived distance; the other was the hypothesis that the extended haptic perception of gap size is specific to a physical invariant lambda of the dynamics of probing. Experiment 1 examined the relation between hepatically perceived gap size and haptically perceived gap distance. No causal connection between the two was found, and all the variance in perceived size was accounted for by lambda. Experiment 2 manipulated the rotational inertia of the probe. Its effect was different for the two perceptions of size and distance, underscoring their independence. The indifference of perceived size to perceived distance was discussed in reference to identifying invariants for both the haptic and the visual perception of size at a distance.

Adult↗

PubMed2001

Intrasaccadic perception.

Mammalian vision has a lowpass frequency characteristic that filters out fast temporal oscillations. Thus, fast-drifting gratings cannot be detected with static eyes, but the same gratings can easily be detected by executing saccades. Because these gratings are invisible under fixation, they are useful for isolating and studying intrasaccadic perception, which is normally masked by presaccadic and postsaccadic perception. We have conducted a number of psychophysical studies using these stimuli, and here we report that intrasaccadic visual processing allows for motion perception, that gratings drifting in the direction of a saccade are perceived as having more contrast than the same gratings drifting in the opposite direction, and that intrasaccadic contrast perception has sufficient grain to allow psychophysical matching of the perceived contrast of gratings drifting in opposite directions. The conditions in which these phenomena occur disprove a recent hypothesis that intrasaccadic motion perception occurs for stimuli processed by the magnocellular system, and our results can be explained by assuming that the temporal lowpass characteristic that accounts for flicker fusion phenomena under vision with static eyes is also operative during saccades.

Contrast Sensitivity↗

PubMed2001

[Auditory perception and language: functional imaging of speech sensitive auditory cortex].

Since the description of cortical deafness, it has been known that the superior temporal cortex is bilaterally involved in the initial stages of language auditory perception but the precise anatomical limits and the function of this area remain debated. Here we reviewed more than 40 recent papers of positron emission tomography and functional magnetic resonance imaging related to language auditory perception, and we performed a meta-analysis of the localization of the peaks of activation in the Talairach's space. We found 8 studies reporting word versus non-word listening contrasts with 54 activation peaks in the temporal lobes. These peaks clustered in a bilateral and well-limited area of the temporal superior cortex, which is here operationally defined as the speech sensitive auditory cortex. This area is more than 4cm long, located in the superior temporal gyrus and the superior temporal sulcus, both anterior and posterior to Heschl's gyrus. It do not include the primary auditory cortex nor the ascending part of the planum temporale. The speech sensitive auditory cortex is not activated by pure tones, environmental sounds, or attention directed toward elementary components of a sound such as intensity, pitch, or duration, and thus has some specificity for speech signals. The specificity is not perfect, since we found a number of non-speech auditory stimuli activating the speech sensitive auditory cortex. Yet the latter studies always involve auditory perception mechanisms which are also relevant to speech perception either at the level of primitive auditory scene analysis processes, or at the level of specific schema-based recognition processes. The dorsal part of the speech sensitive auditory cortex may be involved in primitive scene analysis processes, whereas distributed activation of this area may contribute to the emergence of a broad class of "voice" schemas and of more specific "speech schemas/phonetic modules" related to different languages. In addition, this area is activated by language-related lip movement, suggesting that a multimodal integration of the auditory and the visual information relevant in speech perception occurs at this level. Finally, there is a task-related top-down modulation of the pattern of activation of the speech sensitive auditory cortex which may reflect the fact that the different parts of this structure are connected to different down-stream cortical regions involved in the neural processing of different types of tasks.

Auditory Cortex↗

PubMed2001

Motion perception of short-wavelength sensitive cones in glaucoma using random dots moving.

PURPOSE: To determine whether motion perception of short-wavelength sensitive(SWS) cones is capable of predicting primary open angle glaucoma(POAG) optic neuropathy. METHODS: Motion perceptions of SWS cones were isolated by Blue random dot stimulus displayed on the Yellow background, then the detecting displacement threshold of motion perception from SWS cone in POAG was measured, and compared with the age-matched normal group. RESULTS: The detecting displacement thresholds of motion perception from SWS cones in 8 sites of 15 degrees were all elevated in POAG compared with the normal group. CONCLUSION: These findings suggest that motion perception of SWS cones may reveal preclinical visual nerve damage in early POAG.

Adolescent↗

PubMedDate not supplied

Perception of horizontal head and trunk rotation in patients with loss of vestibular functions.

In patients with loss of vestibular functions, we studied psychophysically the self-motion perception for 'trunk in space' and 'head in space' during various combinations of horizontal head and trunk rotation in the dark. The results were compared to those of normal subjects. For their 'trunk in space' perception, the subjects relied on their internal image of space, derived from the vestibular receptors in the head, and referred their trunk to this as a reference by adding to it a nuchal trunk-to-head signal. The patients, by contrast, always considered the trunk as stationary. Obviously because they were devoid of any space cues, they abandoned or suppressed a neck contribution to their 'trunk in space' perception, which, in fact, would yield an erroneous perception in almost all conditions in the dark. Both the patients and the subjects based their 'head in space' perception on their internal representation of 'trunk in space' and added to this a nuchal head-to-trunk signal. However, the patients' head-to-trunk signal, unlike that of the subjects, was considerably larger than the actual head-to-trunk rotation at low stimulus frequency. We relate this finding to some unconscious modification of their neck muscle activity during passive head rotation. It appears that the patients' gain of the neck input per se is not increased, but rather that subsets of this input are modified according to the particular function they serve.

Adolescent↗

PubMed1996

Specific involvement of human parietal systems and the amygdala in the perception of biological motion.

To explore the extent to which functional systems within the human posterior parietal cortex and the superior temporal sulcus are involved in the perception of action, we measured cerebral metabolic activity in human subjects by positron emission tomography during the perception of simulations of biological motion with point-light displays. The experimental design involved comparisons of activity during the perception of goal-directed hand action, whole body motion, object motion, and random motion. The results demonstrated that the perception of scripts of goal-directed hand action implicates the cortex in the intraparietal sulcus and the caudal part of the superior temporal sulcus, both in the left hemisphere. By contrast, the rostrocaudal part of the right superior temporal sulcus and adjacent temporal cortex, and limbic structures such as the amygdala, are involved in the perception of signs conveyed by expressive body movements.

Adult↗