An fMRI study of the reverse perspective illusion.

"Reverse perspective" is a powerful visual illusion similar to the hollow mask illusion, but more interesting in producing the perception of an illusory motion in a stationary picture. It is caused by conflict between motion parallax and pictorial depth cues in 3D "relief" paintings built with depth inversion. Here we report the measurement of brain activation using fMRI in response to a reverse perspective (RP) object, as well as a normal perspective, 3D-relief object ("shadow-box", SB) and a 2D painting of the same architectural scene. The stimuli were presented to 10 subjects in static and rotating conditions, subtraction of which revealed strong activation of area MT in all three cases. Contrasts between the RP, SB and 2D conditions showed the strongest activation for RP and almost no difference between SB and 2D. The similarity of brain activation between SB and 2D stimuli was interpreted as indicating that observers perceive the illusion of realistic 3D depth in 2D pictures as entirely normal and not qualitatively different from the 3D structure of the shadow-box stimulus. Contrasts between the RP stimulus and either the SB or the 2D stimulus revealed activation of Brodmann Areas 7, 19 and MT (and cerebellar cortex), suggesting the usage of brain regions involved in mental rotation and depth perception in response to the reverse perspective illusion.

Visual evoked potentials and event related potentials in congenitally deaf subjects.

The purpose was to test parameters of visual evoked potentials (VEPs) and of event-related potentials (ERPs) in deaf subjects to verify visual and cognitive CNS functions in a handicapped group of the population. Three types of visual stimuli (with dominating parvocellular or magnocellular system activation or with cognitive tasks) were used in the study. Six deaf persons (4 women, 2 men, mean age 17 years) and 6 persons with normal hearing (sex- and age-matched) were included in this pilot study. In all types of stimulation, latencies and amplitudes of main VEPs and ERPs components were evaluated. No significant latency differences were found. However, significantly reduced amplitudes were found in the occipital area for responses to motion and cognitive stimuli which might be interpreted as a part of functional reorganization of the extrastriate and cognitive cortical areas of deaf subjects.

Reliability and validity of the Test of Visual-Perceptual Skills (Non-Motor)--Revised for Chinese preschoolers.

OBJECTIVE: The reliability and validity of the Test of Visual-Perceptual Skills (Non-Motor)-Revised (TVPS-R) were examined for its usefulness on Hong Kong Chinese preschoolers. METHOD: Content validity was evaluated by six experts. Test-retest reliability, construct validity, and criterion validity were examined on 66 typically developing preschoolers while concurrent validity was examined on these preschoolers plus 52 preschoolers with visual-perception difficulties. RESULTS: Test-retest reliability was high for the total score (intraclass correlation coefficient [ICC] =.88), but not for all subtests (ICC ranged .38 to .77) or for individual items (mean kappa = 0.32). The standard error of measurement (SEM; 1.53) and internal consistency (Cronbach's alpha = .90) were satisfactory. Evidence supporting the test's validity included a significant developmental trend (F = 4.99, p < .001), a lack of gender bias (F = .04, p = .84), and positive known-group differentiation (Wilks's lambda = 52.42, p < .001). The correlation between the Motor-Free Visual-Perceptual Test-Revised composite score and the TVPS-R composite was moderate at r = .60. CONCLUSIONS: When based on the total scores, the TVPS-R was reliable and valid. The use of subtest scores and item scores for decision making or treatment planning is not recommended.

Vision for spatial perception and vision for action: a dissociation between the left-right and near-far dimensions.

Neuropsychological and psychophysical studies have suggested that two distinct visual sub-systems are responsible for perception and action. One of the main psychophysical arguments for this is based on visual illusion such as the Induced Roelofs Effect (IRE), where the location of a visual target presented with an off-centre frame is misperceived when evaluated verbally, but not with a reaching response. This dissociated effect suggests the existence of two independent representations of visual space devoted, respectively, to categorisation and to egocentric localisation of reachable objects. These "cognitive" and "sensorimotor" representations have been assumed to be produced through specific anatomical pathways stemming from the primary visual cortex (respectively, the ventral and dorsal streams). To account for the dissociation found with the IRE, it has been suggested that only the cognitive system is sensitive to contextual information. However this view has been challenged by recent psychophysical studies demonstrating the influence of environmental cues on distance perception and the guiding of movement. In the present study, the IRE is re-evaluated but the near-far and right-left dimensions were dissociated. In agreement with previous findings, our results showed that the IRE in the right-left dimension gives rise to a perceptual misperception of target position with no effect on motor performance. Conversely, when the IRE was induced in the near-far dimension a misperception of the target position affected both perceptual and motor responses. This dissociation indicates that the spatial constraints of the task, and not only the nature of the response, interfere with sensitivity to contextual information leading to visual illusions. It is thus likely that the action system (imputed to the dorsal stream) can be sensitive to contextual information, at least when depth processing is emphasised.

False categories in cognition: the Not-the-Liver fallacy.

This paper reports on an increasingly frequent error committed in cognition research that at best slows progress, and at worse leads to self-perpetuating false claims and misguided research. The error involves how we identify meaningful processes and categories on the basis of data. Examples are given from three areas of cognition: (1) memory, where the misconception has fueled the popular implicit/explicit categories, (2) perception, where the misconception is used to re-evaluate the classic what/where division, and (3) motor skills, where it is used to draw conclusions from patients with Huntington's disease. Reasons for the prevalence of this error, how it relates to double dissociations, and what it suggests about scientific reasoning are offered.

Informational aesthetics measures.

The Birkhoff aesthetic measure of an object is the ratio between order and complexity. Informational aesthetics describes the interpretation of this measure from an information-theoretic perspective. From these ideas, the authors define a set of ratios based on information theory and Kolmogorov complexity that can help to quantify the aesthetic experience.

The induction of anomalous experiences in a mirror-gazing facility: suggestion, cognitive perceptual personality traits and phenomenological state effects.

Previous research suggests that mirror-gazing is efficacious for the facilitation of anomalous experiences. The present experiment tested the hypothesis that the incidence of such experiences is a function of the demand characteristics of the procedure. Participants were randomly allocated to one of two conditions and completed a battery of trait and state measures. Individuals who were given suggestions for anomalous experiences, relative to those who were not, reported a greater number of visual, and a suggestively greater number of vocal, hallucinations. The experience of a descriptively dissociative phenomenological state was the strongest predictor of the reporting of anomalous experiences, but only correlated with the experience of anomalous perceptions in the suggestion condition. Experients of visual apparitions were found to significantly differ from nonexperients in their preference for a visual cognitive style independently of condition.

The developmental test of visual perception-2 normative study on the visual-perceptual function for children in Hong Kong.

This research study intended to investigate the visualperceptual performance of children in Hong Kong by comparing them to the accepted norms on the Developmental Test of Visual Perception-2nd edition. The research examined whether there was significant difference in child's gender, age, and grade. The normative study recruited two hundred and eight-nine children between the ages of 6 and 7 in normal primary schools in Hong Kong. Results indicated that there was a ceiling effect in eye-hand coordination, position in space and spatial relations subtests. Grade differences were found to be significant in all subtests except eye-hand coordination and visual-motor speed. On the other hand, there were no statistical difference in the test scores between boys and girls except on copying and figure-ground subtests. It is concluded that there is a strong need to ensure that norms for visual-perceptual tests are appropriate for the specific cultural groups being assessed.

The Medawar Lecture 2001 knowledge for vision: vision for knowledge.

An evolutionary development of perception is suggested-from passive reception to active perception to explicit conception-earlier stages being largely retained and incorporated in later species. A key is innate and then individually learned knowledge, giving meaning to sensory signals. Inappropriate or misapplied knowledge produces rich cognitive phenomena of illusions, revealing normally hidden processes of vision, tentatively classified here in a 'periodic table'. Phenomena of physiology are distinguished from phenomena of general rules and specific object knowledge. It is concluded that vision uses implicit knowledge, and provides knowledge for intelligent behaviour and for explicit conceptual understanding including science.

Perception of size and lightness of human observers: two criteria for holistic and analytic processing show no correlation in individuals.

Results of a triad-classification task and a multidimensional-scaling (MDS) experiment are compared for individual observers. Both paradigms are designed to reveal whether stimuli are perceived in a holistic or analytic manner (Garner 1974). Subjects differed substantially and consistently in their triad classification pattern. The majority of subjects selected stimuli according to dimensional criteria; this classification type is thought to indicate an analytic stimulus processing. Approximately one third of subjects, however, used a classification according to overall similarity (indicating holistic processing). Except for the very first session, virtually no intermediate classification occurred. This clear separation into two classification types suggests that there actually exist two strongly preferred processing modes. Intraindividual variability between sessions in general was small. In one case, however, a spontaneous switching from a purely dimensional classification to a purely similarity classification occurred. This indicates that the observers have different processing options at their disposal, and are not forced to use a particular processing mode by the stimulus type--as has been supposed in the original concept of integrality/separability of stimuli (Garner 1974). In the MDS experiment also substantial interindividual differences in the "best-fitting" Minkowski metric were found, indicating different processing types. However, for individuals participating in both experiments, there was no correlation between the results of the two experimental paradigms. This is interpreted as a result of the subject's ability to choose between a few perceptual-processing options.

Towards an analytic framework for the visuospatial domain: spatial reference frames, cognitive operations, and neural systems.

This article addresses the confusion in neuropsychological literature on visuospatial function and then proposes an analytic framework towards resolution in the visuospatial domain. Three bodies of literature on visuospatial processing are summarized, and from each is derived an analytic dimension for visuospatial investigation. They are: (1) the frame of space (e.g., egocentric), (2) the definition of spatial operations in cognitive terms, and (3) spatial processing in terms of neural hierarchy and respective neural centers. It is proposed that these dimensions can constitute a working model to clarify the complexity of visuospatial function.

Parallel coding of conjunctions in visual search.

Two experiments investigated whether the conjunctive nature of nontarget items influenced search for a conjunction target. Each experiment consisted of two conditions. In both conditions, the target item was a red bar tilted to the right, among white tilted bars and vertical red bars. As well as color and orientation, display items also differed in terms of size. Size was irrelevant to search in that the size of the target varied randomly from trial to trial. In one condition, the size of items correlated with the other attributes of display items (e.g., all red items were big and all white items were small). In the other condition, the size of items varied randomly (i.e., some red items were small and some were big, and some white items were big and some were small). Search was more efficient in the size-correlated condition, consistent with the parallel coding of conjunctions in visual search.