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PubMed1975

Further studies of a measure of adience-abience: reliability.

Previous studies have suggested adequate reliability for a measure of perceptual adience-abience based on the HABGT in view of significant evidence concerning its construct and predictive validity. The present study explored the test-retest reliability of this scale with 40 process schizophrenics over a two-week interval. Reliability was found to be adequate for both males and females (rho equals .84) for the total scale. The four components of the scale were similarly found to be reliable. No subject changed on retest with respect to adient or abient orientation. Interjudge reliability was very high (rho = .912).

Adult↗
PubMed2000

Bradykinesia in early Huntington's disease.

BACKGROUND: Huntington's disease (HD) is generally considered a hyperkinetic disorder, although hypokinetic features are part of the motor syndrome. Moreover, the striatum is considered to play a key role in initiating and executing motor programs and achieving optimal scheduling in response generation. Controversial results regarding the association between clinical features and markers of progression of the disease might be the result of inadequate restriction of clinical signs to the choreatic syndrome. OBJECTIVE: To determine the relationship of neurologic motor and cognitive indices in patients with HD with intrinsic neuronal loss in the striatum, as measured using raclopride C11 and PET. PATIENTS AND METHODS: A cross-sectional study was performed on 11 patients with mild HD (stages 0-2). Motor (Unified Huntington's Disease Rating Scale [UHDRS], saccadic and tapping speed) and cognitive (verbal fluency, Trail Making Test, Stroop Test, Symbol Digit Modalities Test, Conditioned Associative Learning Test, and silhouette identification and object decision of the Visual Object and Space Perception battery) scores were correlated with raclopride C11 binding. RESULTS: Bradykinesia (a summation of five items of the UHDRS motor scale) was the best predictor for stage, that is, functional capacity, and showed a highly significant relationship with putaminous D2 binding (r = -0.94) and with CAG expansion length x years of age (r = 0.96). The exclusion of two patients with a rigid-akinetic HD variant did not alter these coefficients. Chorea was less well correlated than bradykinesia with D2 binding in all striatal regions. Performance on different cognitive tests, especially in timed tasks, was highly correlated with raclopride C11 binding in caudate nucleus and ventral striatum. CONCLUSION: Loss of D2 binding in the striatum is highly correlated with the deficit in fast motor and cognitive processing in patients with early Huntington's Disease. Thus, impairment of rapid execution of adequate responses to environmental changes seems to be a common manifestation of striatal disorders.

Adult↗
PubMed2006

The role of target elevation in prey selection by tiger beetles (Carabidae: Cicindela spp.).

The elevation of objects in the visual field has long been recognized as a potential distance cue, but it has been demonstrated to a reasonable extent in only four species: humans, frogs, fiddler crabs and backswimmers. Many tiger beetles hunt in flat, sandy areas, and their eyes show "flat-world" adaptations, such as an extended visual streak of higher acuity that corresponds to the horizon. They are therefore possible candidates for the use of elevation as a cue for distance. We tested this empirically and with simulation. In a behavioral prey selection paradigm, in which starved beetles were presented moving prey-targets having different size, speed and elevation, the beetles showed a strong preference for large targets when these were low in the visual field and a weaker preference for small targets when these were near the horizon. Striking of targets above the horizon was reduced compared to sub-horizontal targets, and lacked the size-elevation interaction. We simulated these empirical results with a model that converted elevation to distance, and used distance to estimate the absolute size of the targets. Simulated strike probability was then determined by the similarity between this absolute size and an independently confirmed preferred prey size. The results of the simulation model matched the empirical data as well as the best statistical model of the behavioral results. While some aspects of the model, and the beetles' behavior, differ from the strict geometry of the "elevation hypothesis", our results nevertheless indicate that tiger beetles use elevation to estimate distance to prey, and that it is therefore one of the determinants of prey selection.

Altitude↗
PubMed2001

Classroom contexts: connections between class size and within class grouping.

BACKGROUND: There has been a vigorous debate for many years about the educational effects of class size differences, but even if differences have an impact on pupils' academic progress this still leaves unanswered important questions about what mediates the effect. AIMS: This paper is informed by a classroom contextual perspective, and examines associations between class size and within class groupings (in terms of size and number of groups, adult presence in groups, and type of interaction between grouping members). Age differences in these relationships are also explored. SAMPLES: The quantitative study is based on analysis of 3157 groupings, from 672 Reception, Year 2 and Year 5 classes in 331 schools. The qualitative study was based on 12 classes in 8 case study schools, and questionnaire responses completed by over 100 class teachers. METHODS: Links between size of class and within class groupings were examined on the basis of a 'grouping mapping survey', in which teachers at a given time in the school day provided information on group size and number, adult presence, and type of interaction between pupils, and complementary qualitative analyses of data from teacher-completed questionnaires, and interviews. RESULTS: The number of groups in a class increased with the size of the class. Over all three year groups, small classes had on average just over three groups, while large classes approached six groups. The size of groups in the class decreased with size of class. In class sizes over 25, pupils were more likely to be in a large group of 7-10, while in classes under 25 they were more likely to be in whole class groupings. Qualitative analyses showed that teachers felt that groups of 7-10 pupils had negative educational effects, for example, in terms of the quality and quantity of teaching and children's concentration and contribution in groups. CONCLUSIONS: Results suggest that the effects of class size can be best seen as through the size and number of groups, which will then have implications for learning experiences. So while debate about size of class has often been in terms of reduced size of class resulting in pupil academic gains, it is also important educationally to consider within class grouping size and number, and their effects.

Child↗
PubMed2000

When will the ball rebound? Evidence for the usefulness of mental analogues in appraising the duration of motions.

This study explores the way people appraise the duration of motions when these are only seen momentarily. Three possible theoretical accounts of this skill were developed. The first and second held an analogy between the duration of motions and their visuospatial representations. The third account was based on the existence of a pure chronometrical representation. Three copies of a tennis ball trajectory were created to reproduce the characteristics of the trajectory in terms of each account. The participants first memorized the copy and then used it to appraise the duration of the actual ball trajectory seen only momentarily at the beginning of its flight. The performance of a group given the visuospatial copy paralleled those of a referent group who were allowed to see the actual referent trajectory to memorize its duration. Results showed the importance of visuospatial analogous representations. However, a spatial representation seems to allow better memorization of motion duration.

Adult↗
PubMed1978

Subjective Lorentz transformations and the perception of motion.

It has been known for some 40 years that the perceived velocity of a moving object does not correspond to its physical velocity. It is also known that the perceived length and temporal duration of a moving objects is affected by its physical velocity. In this paper it is argued that such phenomenal distortions can be embedded in a model for motion perception that involves the concepts of moving frames, Lorentz transformations, perceived length contractions, and time dilations. Experimental results support this model and indicate that c, the maximum perceivable velocity of movement, plays a crucial role in determining motion effects.

Humans↗
PubMed1998

No role for motion blur in either motion detection or motion-based image segmentation.

The human contrast sensitivity function is bandpass in form for stimuli of low temporal frequency but low pass for flickering or moving stimuli. Because the loss in sensitivity to moving stimuli is large, images moving on the retina have little perceptible high-spatial-frequency content. The loss of high-spatial-frequency content--often referred to as motion blur--provides a potential cue to motion. The amount of motion blur is a function of stimulus velocity but is significant at velocities encountered by the visual system in everyday situations. Our experiments determined the influence of high-spatial-frequency losses induced by motion of this order on motion detection and on motion-based image segmentation. Motion detection and motion-based segmentation tasks were performed with either spectrally low-pass or spectrally broadband stimuli. Performance on these tasks was compared with a condition having no motion but in which form differences mimicked the perceptual loss of high spatial frequencies produced by motion. This allowed the relative salience of motion and motion-induced blur to be determined. Neither image segmentation nor motion detection was sensitive to the high-spatial-frequency content of the stimuli. Thus the change in perceptual form produced in moving stimuli is not normally used as a cue either for motion detection or for motion-based image segmentation in ordinary situations.

Contrast Sensitivity↗
PubMed1985

Model of human visual-motion sensing.

We propose a model of how humans sense the velocity of moving images. The model exploits constraints provided by human psychophysics, notably that motion-sensing elements appear tuned for two-dimensional spatial frequency, and by the frequency spectrum of a moving image, namely, that its support lies in the plane in which the temporal frequency equals the dot product of the spatial frequency and the image velocity. The first stage of the model is a set of spatial-frequency-tuned, direction-selective linear sensors. The temporal frequency of the response of each sensor is shown to encode the component of the image velocity in the sensor direction. At the second stage, these components are resolved in order to measure the velocity of image motion at each of a number of spatial locations and spatial frequencies. The model has been applied to several illustrative examples, including apparent motion, coherent gratings, and natural image sequences. The model agrees qualitatively with human perception.

Adaptation, Ocular↗
PubMed2006

Integration of local motion is normal in amblyopia.

We investigate the global integration of local motion direction signals in amblyopia, in a task where performance is equated between normal and amblyopic eyes at the single element level. We use an equivalent noise model to derive the parameters of internal noise and number of samples, both of which we show are normal in amblyopia for this task. This result is in apparent conflict with a previous study in amblyopes showing that global motion processing is defective in global coherence tasks [Vision Res. 43, 729 (2003)]. A similar discrepancy between the normalcy of signal integration [Vision Res. 44, 2955 (2004)] and anomalous global coherence form processing has also been reported [Vision Res. 45, 449 (2005)]. We suggest that these discrepancies for form and motion processing in amblyopia point to a selective problem in separating signal from noise in the typical global coherence task.

Adult↗
PubMed1986

Determining the kinematic parameters of a moving imaging sensor by processing spatial and temporal intensity changes.

A method is presented that determines the motion parameters of an imaging sensor by evaluating the spatial and temporal intensity changes in the image plane. It is not necessary to compute the optical flow. If the environment in the field of view is described parametrically, constraint equations between the kinematic parameters and the intensity changes can be derived. Linear solutions of these equations are the so-called pure parameters, which are nonlinear functions of the motion parameters. These quantities are the roll, pitch, and yaw rate, the angle of attack and the angle of yaw, and orientation parameters. They can be obtained directly by solving a 3 X 3 eigenvalue problem. The algorithm was implemented and applied to artificial and natural image sequences. An error and covariances analysis shows that the method is robust and accurate enough for autonomous navigation.

Algorithms↗
PubMed1987

Cooperative phenomena in the perception of motion direction.

A percept of global coherent motion can result from the combination of many different localized motion vectors. We report here evidence of hysteresis in the perception of this global motion, obtained with random-dot cinematograms. The hysteresis characteristics are relatively robust with respect to changes in dot density, display area, and location. Changing the directional content of the stimulus, however, did alter the hysteresis profile in a manner consistent with a model incorporating cooperative interactions among direction-selective motion mechanisms. Our results lend further support to a cooperative interpretation of motion results lend further support to a cooperative interpretation of motion perception in random-dot cinematograms.

Humans↗
PubMed1991

Perceived speed and direction of complex gratings and plaids.

Measurements of perceived speed were obtained for a variety of drifting simple and complex gratings, and measurements of perceived speed and direction were obtained for plaids. For sine gratings, perceived speed falls off at high spatial frequencies, the effect of spatial frequency being greatest at high speeds. Speed matches obtained from a variety of one-dimensional complex gratings are in some cases consistent with a simple averaging of the discrepant speeds signaled by their spatial Fourier components when seen alone. However, in other cases the results do not fit such an interpretation but suggest the involvement of a mechanism other than Fourier decomposition and recombination. Measurements of the perceived speed of plaids suggest that the observed spatial-frequency-dependent variations in encoded speed of gratings arise largely at a low level, before the aperture problem is solved. Measurements of the perceived direction of plaids whose components are of different spatial frequencies and hence have different perceived speeds show large deviations from the direction predicted by the intersection-of-velocity-constraints model [Nature 300, 523 (1982)] and are suggestive of a revised two-stage model in which the computation of pattern direction is based on the (sometimes disparate) perceived speeds of the components rather than their actual speeds.

Humans↗