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PubMed2006

Priming and binding in and across perception and action: a correlational analysis of the internal structure of event files.

Individual performance was compared across three different tasks that tap into the binding of stimulus features in perception, the binding of action features in action planning, and the emergence of stimulus-response bindings ("event files"). Within a task correlations between the size of binding effects were found within visual perception (e.g., the strength of shape-location binding correlated positively with the strength of shape-colour binding) but not between perception and action planning, suggesting different, domain-specific binding mechanisms. To some degree, binding strength was predicted by priming effects of the respective features, especially if these features varied on a dimension that matched the current attentional set.

Analysis of Variance↗

PubMed1986

Disruptive effects of auditory signal delay on speech perception with lipreading.

The effect of auditory signal delay on audio-visual perception of videotaped sentence lists by Ss with normal hearing was measured. The test material consisted of sentences read by a man, with or without a picture representing as context one of the key words in each sentence. In Exper. I, 12 Ss (6M, 6F), inexperienced with lipreading, were presented test material in the audio-only (A), visual-only (V) and audio-visual (AV) modes. Speech signals were presented at 0 or -10 db S/N re a multitalker babble fixed at 60 dbA. The audio signal was delayed (re visual signal) in 6 steps from 0-300 msec. Exper. II repeated Exper. I with 6 Ss (2M, 4F) familiar with lipreading; the speech signal was presented at -5 db S/N and 4 audio delays from 0-240 msec. While these Ss performed better in the V mode than those in Exper. I, the main effects of context and delays were similar. The disruptive effect of the audio delay on speech perception with lipreading (AV mode) was a function of S/N, being relatively more disruptive at the worse S/N, but it was not significant for delays up to a range of 80-120 msec. The results are in agreement with the theory (McGrath and Summerfield, J. Acoust. Soc. Am., 1985, 77, 678-685) that sensitivity to audio-visual desynchrony is significant only at a syllabic level in connected speech. The results further imply that moderate delays of up to 80 msec introduced by speech-processing aids for lipreading, as for cochlear-implanted patients, will not interfere with the advantages of providing the auditory information.

Acoustic Stimulation↗

PubMed2006

Concurrent TMS-fMRI and psychophysics reveal frontal influences on human retinotopic visual cortex.

BACKGROUND: Regions in human frontal cortex may have modulatory top-down influences on retinotopic visual cortex, but to date neuroimaging methods have only been able to provide indirect evidence for such functional interactions between remote but interconnected brain regions. Here we combined transcranial magnetic stimulation (TMS) with concurrent functional magnetic resonance imaging (fMRI), plus psychophysics, to show that stimulation of the right human frontal eye-field (FEF) produced a characteristic topographic pattern of activity changes in retinotopic visual areas V1-V4, with functional consequences for visual perception. RESULTS: FEF TMS led to activity increases for retinotopic representations of the peripheral visual field, but to activity decreases for the central field, in areas V1-V4. These frontal influences on visual cortex occurred in a top-down manner, independently of visual input. TMS of a control site (vertex) did not elicit such visual modulations, and saccades, blinks, or pupil dilation could not account for our results. Finally, the effects of FEF TMS on activity in retinotopic visual cortex led to a behavioral prediction that we confirmed psychophysically by showing that TMS of the frontal site (again compared with vertex) enhanced perceived contrast for peripheral relative to central visual stimuli. CONCLUSIONS: Our results provide causal evidence that circuits originating in the human FEF can modulate activity in retinotopic visual cortex, in a manner that differentiates the central and peripheral visual field, with functional consequences for perception. More generally, our study illustrates how the new approach of concurrent TMS-fMRI can now reveal causal interactions between remote but interconnected areas of the human brain.

Adult↗

PubMed2004

The effects of task and saliency on latencies for colour and motion processing.

In human visual perception, there is evidence that different visual attributes, such as colour, form and motion, have different neural-processing latencies. Specifically, recent studies have suggested that colour changes are processed faster than motion changes. We propose that the processing latencies should not be considered as fixed quantities for different attributes, but instead depend upon attribute salience and the observer's task. We asked observers to respond to high- and low-salience colour and motion changes in three different tasks. The tasks varied from having a strong motor component to having a strong perceptual component. Increasing salience led to shorter processing times in all three tasks. We also found an interaction between task and attribute: motion was processed more quickly in reaction-time tasks, whereas colour was processed more quickly in more perceptual tasks. Our results caution against making direct comparisons between latencies for processing different visual attributes without equating salience or considering task effects. More-salient attributes are processed faster than less-salient ones, and attributes that are critical for the task are also processed more quickly.

Attention↗

PubMedDate not supplied

Aging, texture segmentation, and exposure duration: evidence for a deficit is preattentive processing.

Younger and older observers were asked to detect the presence and identify the orientation of an orientation-based texture target presented at durations ranging from 15 to 75 ms. In Experiment 1a, an age by duration interaction indicated that older adults were less able to process the displays at short durations. In Experiment 1b, a group of younger adults was given the task under conditions designed to simulate age-related changes in retinal illuminance. Their performance was independent of luminance, and was still superior to that of older adults in Experiment 1a. Several mechanisms are potential contributors to these age deficits in lower-level processing that can influence higher-level visual perception.

Adolescent↗

PubMed1992

Differences in vividness ratings of perceived and imagined patterns.

The present research focuses on the different subjective experiences evoked by perceived and imagined matrices of letters of the alphabet. In three experiments adult subjects were asked to rate the vividness of a letter included in a matrix of letters which varied due to manipulations in colour, rotation and movement. Subjects were asked to observe (perceptual modality), draw and observe (drawing modality), retrieve (memory modality) or imagine (imagery modality) the matrices. For some manipulations of the critical letter (in particular, 45 degrees inclination and high contrast colour), the perceptual modality produced comparatively higher vividness ratings than the other two modalities. The perceptual effect of inclination was also duplicated with the memory modality group. It is argued that different visual processes, either immediate and pre-attentive, or sequential and attentive, may be operating under voluntary control. Although visual imagery varies in some ways from immediate visual perception, the similarities found, between the drawing and imagery modalities, on the one hand, and the perceptual and memory modalities, on the other hand, suggest that they share some common underlying processes.

Adult↗

PubMed1976

Efficacy of the Visual Retention Test as a group-administered instrument for young children.

Group and individual administrations of the Revised Visual Retention Test to 84 primary-grade children, matched on chronological age and IQ, were demonstrated to be comparable. Form C of the test was used for memory and copy administrations, together with a multiple-choice version. No significant difference was obtained between treatments on memory, copy, or multiple-choice. The group testing procedure appears to provide a valid technique for screening intact classroms for visual perception, memory, and constructive deficits. Further research with the various forms and administrations is suggested to determine the educational correlates of performance.

Age Factors↗

PubMed1980

Using color to design effective projected transparencies.

In the design of projected transparencies, aesthetics usually govern color selection. However, the perceptual consequences of color use should be considered as well. Studies on the effects of color on visual perception and attention to them in the psychological literature are reviewed. The findings are discussed and applied to the problem of selecting color for projected transparencies.

Arousal↗

PubMed1990

Projective invariance and picture perception.

Four experiments test the assumption that, in the visual perception of pictures, observers have reliable and direct access to the equivalence of shapes in projective geometry. The assumption is that perception of projective equivalence is the basis of shape constancy ('the projective thesis'). Observers matched or reproduced abstract planar shapes under conditions of rotation in the picture plane, and pictured rotation in depth. Departure from projective equivalence was assessed in each study by measuring the planar analogue of cross ratio. Projective equivalence was not found to be perceived uniformly where Euclidean equivalence was not judged uniformly, either in recognition tasks or in production tasks. When the projective thesis is put to a suitably general test, confidence in the thesis is undermined.

Adult↗

PubMed1990

Visual properties of neurons in the thalamus and striopallidar complex of the human brain.

In parkinsonian patients diagnosed and treated with the aid of long-term intracerebral electrodes, neuronal impulse activity (NIA) was recorded in different nuclei of the thalamus and striopallidar complex during visual testing for orientation sensitivity. Neuronal populations responding only to the presented stimuli with specific angular orientations have been revealed. Orientation-selective neurons have been found with significant responses in NIA observed to the same angular orientations of stimuli during 90 degrees head tilts. It is hypothesized that the visual perception constancy can be maintained with the participation of cerebral nuclei containing such neurons on the basis of convergence of motor, somatosensory and visual information.

Action Potentials↗

PubMed2004

Visual object recognition deficits in early Parkinson's disease.

The nature of the visual perception deficits in Parkinson's disease (PD) has remained unclear. The present study explored whether there emerge deficits in the different stages of visual object recognition in early PD. Twenty-eight patients and 14 healthy controls were studied. A set of reaction time tasks were applied to measure the different stages of object recognition. The results indicate some selective problems in both basic perceptual and semantic visual processing at an early stage of cognitive deterioration in PD.

Aged↗

PubMed1998

Neuronal correlates of visibility and invisibility in the primate visual system.

A brief visual target stimulus may be rendered invisible if it is immediately preceded or followed by another stimulus. This class of illusions, known as visual masking, may allow insights into the neural mechanisms that underlie visual perception. We have therefore explored the temporal characteristics of masking illusions in humans, and compared them with corresponding neuronal responses in the primary visual cortex of awake and anesthetized monkeys. Stimulus parameters that in humans produce forward masking (in which the mask precedes the target) suppress the transient on-response to the target in monkey visual cortex. Those that produce backward masking (in which the mask comes after the target) inhibit the transient after-discharge, the excitatory response that occurs just after the disappearance of the target. These results suggest that, for targets that can be masked (those of short duration), the transient neuronal responses associated with onset and turning off of the target may be important in its visibility.

Animals↗

PubMed2005

Misrouting of the optic nerves in albinism: estimation of the extent with visual evoked potentials.

PURPOSE: In human albinism a part of the temporal retina projects abnormally to the contralateral hemisphere. An objective VEP procedure to quantify the extent of the abnormality was devised. METHODS: Monocular VEPs were recorded in 16 subjects with albinism and in 16 controls from occipital electrodes to pattern-onset stimulation in 1 of 10 adjacent rectangular apertures along the horizontal meridian covering a total of +/-27 degrees. For each eye interhemispheric difference potentials were calculated and correlated with each other to assess the lateralization of the responses: positive and negative correlations indicate lateralization on same or opposing hemispheres, respectively. Different stimulus conditions were compared to assess the sensitivity and specificity of the procedure for the detection of the misrouting of visual projections in albinism. RESULTS: Locations that were affected by the projection abnormality were detected with a specificity of 100% and an average sensitivity of 97%. In the 16 subjects with albinism tested, the abnormal projection was confined to the central retina and varied in extent between subjects (2 degrees - 15 degrees; median, 8 degrees). The extent did not appear to be correlated with horizontal nystagmus amplitude or visual acuity. CONCLUSIONS: Because of the great interindividual variability of the projection abnormality, studies of the contribution of the abnormally projecting retina to visual perception must be preceded by the localization of the abnormality. This VEP procedure allowed the authors to identify, with high sensitivity and specificity, visual field locations that are affected by the projection abnormality.

Adult↗

PubMed1999

A comparison of Tactaid II+ and Tactaid 7 use by adults with a profound hearing impairment.

OBJECTIVE: To evaluate and compare use of the Tactaid II+ and the Tactaid 7, in terms of speech perception, by adults with a hearing impairment. DESIGN: Eight adults used one device daily for approximately 10 wk and attended seven training sessions. Performance was measured with tests of phonetic contrast perception, closed-set vowel and consonant identification, word and phoneme recognition in monosyllabic word lists, word recognition in sentences and speechtracking rate. A questionnaire was also administered. The protocol was repeated with the alternative device. RESULTS: With each device, the group discriminated most phonetic contrasts at better-than-chance levels and demonstrated somewhat enhanced visual or auditory-visual perception when measured in terms of vowel identification, monosyllabic word recognition and speechtracking rate. An increase in speechtracking rate was also demonstrated for some individuals. Subjects generally reported little subjective improvement in speech perception and production, but were satisfied with the physical attributes of each device. Five of six subjects preferred the Tactaid 7. CONCLUSIONS: The Tactaid II+ and the Tactaid 7 provided suprasegmental and segmental information, enabling the group to discriminate phonetic contrasts and improve their perception of some speech materials. No consistent advantage was found for either device, thought most subjects preferred the Tactaid 7. Alternatives likely to provide a greater benefit to communication should be considered before a Tactaid fitting.

Acoustic Stimulation↗

PubMed1982

The interpretation of biological motion.

The term biological motion has been coined by Johansson (1973) to refer to the ambulatory patterns of terrestrial bipeds and quadripeds. In this paper a computational theory of the visual perception of biological motion is proposed. The specific problem addressed is how the three-dimensional structure and motions of animal limbs may be computed from the two dimensional motions of their projected images. It is noted that the limbs of animals typically do not move arbitrarily during ambulation. Rather, for anatomical reasons, they typically move in single planes for extended periods of time. This simple anatomical constraint is exploited as the basis for utilizing a "planarity assumption" in the interpretation of biological motion. The analysis proposed is: (1) divide the image into groups of two or three elements each; (2) test each group for pairwise-rigid planar motion; (3) combine the results from (2). Fundamental to the analysis are two "structure from planar motion" propositions. The first states that the structure and motion of two points rigidly linked and rotating in a plane is recoverable from three orthographic projections. The second states that the structure and motion of three points forming two hinged rods constrained to move in a plane is recoverable from two orthographic projections. The psychological relevance of the analysis and possible interactions with top down recognition processes are discussed.

Gait↗

PubMed1996

The recognition potential and conscious awareness.

The idea that conscious awareness of a recognizable image is necessary for it to evoke the recognition potential (RP) was tested by asking bilingual subjects to selectively attend to superimposed English and Chinese word images. The subjects detected most of the words in the attended language, but were largely oblivious of words in the non-attended language. Attended word images evoked the RP. Non-attended words did not. RP latency was less for Chinese than for English words. This provided a basis for inferring which language a subject was trying to read when valid English and Chinese words were both present. A subject was looking for Chinese if the latency was short and for English if it was long. The results showed that selective attention had a powerful effect on the RP. They supported the idea that conscious awareness is necessary for evoking it, though they did not rule out the theoretical possibility that some method not yet tested could be found that would block conscious awareness without blocking the RP. The sensitivity of the RP to what a subject is trying to see and its low variance seem to provide advantages for studying visual perception. It provides a short latency indicator of image processing that merits further investigation. Use of it may lead to a better understanding of visual perceptual processes.

Adult↗

PubMed1993

The role of features in preattentive vision: comparison of orientation, motion and color cues.

Arrays of lines or blobs were used to investigate the role of features vs feature contrast in preattentive vision. This study continues earlier work on orientation cues and extends it into the dimensions of motion and color. Tests were performed on patterns displaying continuous feature gradients, i.e. continuous variation, from element to element, in either line orientation, direction of motion, or color. In different series of experiments, the following four aspects of visual perception were investigated: (i) detection of a salient target ("odd man out" paradigm), (ii) segmentation of texture fields, (iii) search strategies for given targets, and (iv) figure-ground discrimination by grouping. Features were, in general, not found to play an important role in these tasks and performance was instead related to feature contrast. Only in the case of color did performance also depend upon hue, i.e. feature properties themselves. Whereas in all dimensions tested pop-out ("saliency") and segmentation were obtained from target or border elements whose local feature contrast was well above the level of variation elsewhere in the pattern, performance in the two latter tasks differed between orientation, motion, and color. In search, orientation targets were detected quickly when sufficiently distinct from their neighbors, but were apparently searched for serially if feature contrast was similar to that of other elements nearby. Color targets, however, were always detected fast in these patterns, independently of local feature contrast. Also, the perceived grouping of orientation or motion defined targets depended only on local feature contrast and not on the similarity of target elements. In fact, figures of dissimilar elements were seen as easily as figures of similar elements, indicating that, in these dimensions, stimulus coherence is not essential for the discrimination of figure and ground. For color, however, figures made up of the same targets were always seen slightly better than figures composed of different colors.

Adolescent↗

PubMed2004

Wider recognition in peripheral vision common to different subtypes of dyslexia.

Italian children (n = 125) were classified into dyslexics, poor readers and ordinary readers. The dyslexics were further classified into the Boder and Bakker subtypes. The children were tested with the form-resolving field (FRF), which measures central and peripheral visual recognition. Dyslexics show higher correct identification of letters in the periphery, supporting the notion of a different distribution of lateral masking. A numerical characterization of individual FRFs--C2R--reliably distinguishes between dyslexics and ordinary readers. The wider distribution of recognition, similar across the various subtypes of dyslexia, suggests a general characteristic of visual perception, and possibly a different visual-attentional mode.

Adolescent↗