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PubMed1997

Radial motion looks faster.

Current models of motion perception depend on unidirectional motion-sensitive mechanisms that provide local inputs for complex pattern motion, such as optic flow. To test the generality of such models, we asked observers to compare the speed of radial gratings with the translational speed of vertical gratings. The speed of the radial gratings was consistently overestimated by 20-60% relative to that of translating gratings that were identical in all other respects. The speed bias was not associated with a general spatial or temporal processing bias, nor with the high relative speed of points about the center of expansion/contraction. The bias increased non-linearly with the size of sectors of the radiating pattern exposed. As the motion of the two patterns was locally identical but judged differently, the apparent speed of both kinds of motion cannot be served by any mechanism, nor described by any model, that is based entirely on local motion signals. We speculate that the greater apparent speed of the radial motion has to do with apparent motion in depth.

Humans↗
PubMed1999

Optimal spatial frequencies for discrimination of motion direction in optic flow patterns.

Spatial frequency tuning functions were measured for direction discrimination of optic flow patterns. Three subjects discriminated the direction of a curved motion path using computer generated optic flow patterns composed of randomly positioned dots. Performance was measured with unfiltered patterns and with patterns that were spatially filtered across a range of spatial frequencies (center spatial frequencies of 0.4, 0.8, 1.6, 3.2, 6.4, and 9.6 c/deg). The same subjects discriminated the direction of uniform, translational motion on the fronto-parallel plane. The uniform motion patterns were also composed of randomly positioned dots, that were either unfiltered or filtered with the same spatial filters used for the optic flow patterns. The peak spatial frequency was the same for both the optic flow and uniform motion patterns. For both types of motion, a narrow band (1.5 octaves) of optimal spatial frequencies was sufficient to support the same level of performance as found with unfiltered, broadband patterns. Additional experiments demonstrated that the peak spatial frequency for the optic flow patterns varies with mean image speed in the same manner as has been reported for moving sinusoidal gratings. These findings confirm the hypothesis that the outputs of the local motion mechanisms thought to underlie the perception of uniform motion provide the inputs to, and constrain the operation of, the mechanism that processes self motion from optic flow patterns.

Computer Graphics↗
PubMed1999

Revisiting motion repulsion: evidence for a general phenomenon?

Previous studies have found large misperceptions when subjects are reporting the perceived angle between two directions of motion moving transparently at an acute angle, the so called motion repulsion. While these errors have been assumed to be caused by interactions between the two directions present, we reassessed these earlier measurements taking into account recent findings about directional misperceptions affecting the perception of single motion (reference repulsion). While our measurements confirm that errors in directional judgments of transparent motions can indeed be as big as 22 degrees we find that motion repulsion, i.e. the interaction between two directions, contributes at most about 7 degrees to these errors. This value is comparable to similar repulsion effects in orientation perception and stereoscopic depth perception, suggesting that they share a common neural basis. Our data further suggest that fast time scale adaptation and/or more general interactions between neurons contribute to motion repulsion while tracking eye movements play little or no role. These findings should serve as important constraints for models of motion perception.

Adaptation, Psychological↗
PubMed1999

Stereoscopic (cyclopean) motion sensing.

This paper reviews literature on the motion processing of dynamic change in binocular disparity, called stereoscopic (cyclopean) motion. Studies investigating the visual processing of stereoscopic motion in the Z-axis, stereoscopic motion in the X/Y plane, and cyclopean motion are discussed. It is concluded that stereoscopic motion is processed by a motion-sensing system composed of special-purpose mechanisms that function like low-level motion sensors. For animals with binocular vision, low-level motion processing may involve, at least in part, stereoscopic processing.

Animals↗
PubMed2000

Illusory spatial offset of a flash relative to a moving stimulus is caused by differential latencies for moving and flashed stimuli.

A flash that is presented adjacent to a continuously moving bar is perceived to lag behind the bar. One explanation for this phenomenon is that there is a difference in the persistence of the flash and the bar. Another explanation is that the visual system compensates for the neural delays of processing visual motion information, such as the moving bar, by spatially extrapolating the bar's perceived location forward in space along its expected trajectory. Two experiments demonstrate that neither of these models is tenable. The first experiment masked the flash one video frame after its presentation. The flash was still perceived to lag behind the bar, suggesting that a difference in the persistence of the flash and bar, does not cause the apparent offset. The second experiment employed unpredictable changes in the velocity of the bar including an abrupt reversal, disappearance, acceleration, and deceleration. If the extrapolation model held, the bar would continue to be extrapolated in accordance with its initial velocity until the moment of an abrupt velocity change. The results were inconsistent with this prediction, suggesting that there is little or no spatial compensation for the neural delays of processing moving objects. The results support a new model of temporal facilitation for moving objects whereby the apparent flash lag is due to a latency advantage for moving over flashed stimuli.

Humans↗
PubMed1975

Minimal brain Dysfunction.

Because of the prevalence in our society of children labeled with the term minimal brain dysfunction; physicians who treat children must develop a point of view toward the syndrome and a working procedure for assisting affected children. An approach to this problem can be divided into two parts: detection of somatic disorders and comprehensive management of school problems. The detection of somatic disorders that may have produced or substantially contributed to the school problem requires conventional medical skills for recognition and treatment. Comprehensive management of school problems requires a broader approach by the physician; including counseling of the parents regarding adverse family interactions, advice about educational resources and consideration of the question of drug therapy for behavioral disorders. In all instances parents should be able to rely on the physician to act as a scientific source of guidance on the merits of the plethora of therapies directed toward the child with learning disorders. The ability to function competently in all of these areas will enable the physician to provide a service for children and their families that may profoundly affect their lives.

Attention Deficit Disorder with Hyperactivity↗
PubMed2003

Effects of lesions of the cerebellar oculomotor vermis on eye movements in primate: binocular control.

The effects of lesions of the dorsal 'oculomotor' cerebellar vermis on binocular oculomotor functions in three monkeys were examined. Prominent findings included (1) a convergence bias during monocular fixation, i.e., an 'esodeviation' in the absence of disparity cues, (2) a loss of comitancy, i.e., alignment varies more with orbital position, (3) abnormal saccade yoking producing saccade disconjugacy, and (4) defects in prism-induced phoria adaptation. There was also a suggestion of a disturbance in the dynamic properties of disparity-induced vergence. These findings point to a role for the 'oculomotor' vermis in binocular aspects of the control of eye movements.

Adaptation, Physiological↗
PubMed2003

Interpretations of child compliance in individuals at high- and low-risk for child physical abuse.

OBJECTIVE: Our studies compared individuals at high- and low-risk for child physical abuse on measures of social information processing. METHOD: Two studies were conducted using similar methods. Twenty-eight childless women in Study 1 and 36 mothers in Study 2 read vignettes of parent-child interactions in which the child's level of compliance was difficult to interpret. Participants were asked a series of questions about the child's behavior and their own reactions. RESULTS: Accuracy and bias in identifying compliant behavior were assessed using a signal detection paradigm. In both samples, high- and low-risk participants did not differ in their overall accuracy in identifying children's behaviors. However, they used different evaluation standards such that high-risk participants were biased toward seeing more noncompliance and low-risk participants were biased toward seeing more compliance. High- and low-risk participants also made different types of errors in interpreting children's behavior. Low-risk participants were more likely to misinterpret noncompliant behavior as compliant, and there was a trend for high-risk participants to not perceive compliant behavior when it occurred. There were no differences in reported disciplinary responses in either study and the results for affective reactions were mixed. CONCLUSIONS: Specific differences in social information processing between high- and low-risk individuals replicated across samples, suggesting a reliable association between evaluation standards and risk of child physical abuse. However, the absence of differences in reported discipline and inconsistent findings on affective reactions indicate the need to identify the mechanism through which cognition influences parenting behavior.

Adolescent↗
PubMed1998

A bedside test to determine motion stereopsis using the Pulfrich phenomenon.

OBJECTIVE: Many diseases induce asymmetric delays in the visual pathway, resulting in a spontaneous Pulfrich phenomenon (PP). The PP is a visual stereoillusion that may cause difficulties in persons when traveling in cars, crossing the road, or playing ball games. The authors developed and tested a simple new bedside procedure to detect PP. DESIGN: A case series. PARTICIPANTS: Disease simulation in 2 normal subjects and 18 patients with optic neuritis (ON) was examined. Ninety normal subjects were studied to determine normal range of PP. INTERVENTION: The new test, called swinging pen test (SPT), is performed by oscillating a pen by hand. The SPT was compared to a gold standard, a mechanical pendulum (MP). MAIN OUTCOME MEASURES: The authors measured simulated PP in two normal subjects and PP in 18 patients with ON and 90 normal control subjects. The Pearson product-moment correlation (r) and the Spearman rank correlation (rs) between SPT and MP were calculated. RESULTS: The magnitudes of simulated PP determined with the SPT and the MP correlated well (r = 0.92, P < 0.005, and r = 0.96, P < 0.001). Correlation also was good in patients with ON (rs = 0.90, P < 0.05). The positive predictive value of the SPT was 100%, and the negative predictive value was 92%. The PP was absent in all control subjects testing with either pendulum. The normal range for PP varied from -1.40 to 1.52 msec. For the SPT, the intraobserver variability coefficient was 8.2%, and the interobserver variability coefficient was 10.5%. CONCLUSIONS: The authors believe that SPT will be of value to clinicians on bedside evaluation of motion stereopsis dysfunctions. The normal range of PP was approximately +/- -1.5 msec (approximately +/- -1.5 cm), corresponding to a 0.3-log unit neutral density filter).

Acute Disease↗
PubMed1998

Adaptation of visually guided behavior during reversed vision in schizophrenia: a preliminary study.

This preliminary study evaluated the adaptation of visually guided behavior to reversed vision in schizophrenia. The study included 54 patients who met DSM-III-R criteria for schizophrenia. Visuomotor reaction times (VRTs) during reversed vision were measured in six blocks of 35 consecutive trials. The VRTs of schizophrenics were compared with those of normal subjects. A good fit (R2 = 0.9981) for the adaptation process of VRTs during reversed vision was found with the equation y = 1030 + 1499/x, where x is the order of the block and y is the group mean VRT for each block. The VRTs in schizophrenics were significantly slower than those in normal subjects. However, the adaptation process to reversed vision essentially did not differ from normal. The adaptation of visually guided behavior during reversed vision may involve procedural learning; this task may thus be useful in evaluating such learning. The VRTs during reversed vision may be related to some aspects of symptoms in the patient with schizophrenia and may also be useful in predicting clinical outcome.

Adult↗
PubMed2003

When visuo-motor incongruence aids motor performance: the effect of perceiving motion structures during transformed visual feedback on bimanual coordination.

Two experiments are reported in which bimanual coordination tasks were performed under correct and transformed visual feedback conditions. Participants were to generate cyclical line-drawing patterns, with varying degrees of coordinative stability, while perceiving correct or transformed visual information of the trajectories on a screen. Visuo-motor transformations that dissociated the perceived movement direction from the actually generated direction, were applied to one or both limbs, resulting in varying degrees of perceptual grouping power. The transformed feedback did not influence the most stable coordination patterns (in-phase) whereas the accuracy and/or stability of the less stable coordination patterns (anti-phase and particularly orthogonal) benefited from particular visual feedback manipulations, i.e. when coherently grouped visual motion structures emerged, the quality of coordination improved significantly. These findings indicate that perceptual transformations aid the production of more complex coordination patterns, thereby underscoring the importance of perception-action coupling in bimanual coordination.

Adult↗
PubMed2003

Nociceptive processing in the human brain of infrequent task-relevant and task-irrelevant noxious stimuli. A study with event-related potentials evoked by CO2 laser radiant heat stimuli.

Laser evoked potentials (LEPs) are nociceptive-related brain responses to activation of cutaneous nociceptors by laser radiant heat stimuli. We previously showed that LEP amplitude during the P2 period (approximately 400 ms) was increased by rare noxious stimuli, inside and outside the focus of spatial attention. It was postulated that this effect reflected a P3a response indexing an involuntary shift of attention. In the present study, LEPs were recorded in a three-stimulus oddball paradigm, commonly used to evoke P3a (or novelty-P3). CO(2) laser-induced noxious stimuli were delivered on one hand (80%, frequent). Two series of rare stronger-intensity deviant stimuli were randomly intermixed: target stimuli (10%) were delivered on the same hand while distractor stimuli (10%) were delivered on the other hand. Subjects were instructed to count targets. During an additional session, strong stimuli were delivered alone on one hand without instruction (100%, no-task stimuli). All stimulus types evoked a first positivity around 360 ms (P360). Targets and distractors elicited a late positive complex (LPC) around 465-500 ms. Topography of LPC to distractors was central and significantly more anterior than that of LPC to targets. Distractor LPC corresponds to P3a (or novelty-P3) indexing an involuntary orientation of attention toward an unexpected new/deviant event. It suggests that at least an early part of the LEP positivity (P360) is independent of P3-activities.

Adult↗
PubMed1998

Motion sickness amelioration induced by prism spectacles.

A side effect of the prescription of prism glasses according to the principle of Utermöhlen to improve mechanical reading skills of certain types of learning disabled children was the alleviation of car sickness. Besides a decrease in reported symptoms after prescription of these glasses, the effect is quantified by a decrease in estimated number of emeses per year per patient. A placebo effect is unlikely because alleviation of car sickness was not the original intention of the prescription, and the symptoms returned as soon as the spectacles were discontinued.

Adolescent↗
PubMed2003

Flexibility of vestibulo-ocular reflex adaptation to modified visual input in human.

The vestibulo-ocular reflex (VOR) serves to keep images relatively stable on the retina. To maintain appropriate performance and minimize image slip throughout life, VOR is subjected to long-term adaptive regulation by visual input. It has been reported that adaptive changes in VOR gain (eye velocity/head velocity) are evoked either by fitting subjects with magnifying, miniaturizing, or reversing spectacles during normal behavior, or by moving a large visual field in or out of phase relative to the subject's head movement. The changes in VOR gain are frequency selective. Here, we examine the extent of VOR gain flexibility by causing VORs of similar direction to undergo different behavioral gain changes. Nine healthy adults participated in the study, ranging in age from 24 to 38 years (mean: 26 years) and with no history of neurotological symptoms. All subjects were clinically normal according to a screening battery that included combined neurologic and otologic physical examinations. Horizontal and vertical eye positions were recorded by bitemporal DC-coupled electro-oculography (EOG). The subject sat in a rotating chair. The axis of rotation of the body was always earth-vertical, with the interaural axis crossing the axis of rotation of the chair. The head was pointed 20 degrees downwards in all experiments and stabilized in this position using a chin rest. The chair was surrounded by a half-cylindrical optokinetic screen (78 cm in diameter) placed in front of the subject, onto which random dot patterns were projected. Goggles were used to ensure that the subject was in complete darkness during both pre- and postadaptation periods. The chair was rotated sinusoidally at maximum amplitude of 30 degrees or 60 degrees : for 30 degrees the stimulation was at 0.1, 0.2, 0.3, and 0.4 Hz; for 60 degrees it was at 0.1, 0.2, and 0.3 Hz. VOR adaptation was obtained by inducing a retinal slip velocity by short-term alteration of the visual input of the large field; this change was produced by a combination of sinusoidal head rotation and the random dot patterns. In each adaptation session, the sinusoidal head rotation was either at 0.1 or 0.3 Hz and the amplitude was 30 degrees. The random dot pattern was synchronized with sinusoidal head rotation in the same direction (x0 experiment) to make the retinal slip zero, and in the opposite direction to make the retinal slip twofold (x2 experiment). Therefore, a total of four adaptation protocols were tested. The subjects were asked to fixate on a single dot with the eyes straight-ahead in the x0 experiment, and follow it within random dot patterns in the x2 experiment. Each adaptation session lasted for 30 min. Two adaptation experiments were performed on each subject once per day. The averages of VOR gain and phase lag were calculated using Fourier analysis. Seven of the subjects who participated in the x2 adaptation experiment at 0.3 Hz and 30 degrees amplitude showed a steady increase of VOR gain within a couple of trials. One of the remaining two subjects showed a decrease in VOR gain in all the three trials, and the other subject showed a VOR gain increase in three trials and decrease in two trials. In the x2 adaptation experiment at 0.3 Hz and 30 degrees amplitude (peak velocity: 28 degrees /s), the percentage gain change ((post-pre)/pre) was 133% at the same stimulation and 100% at 0.4 Hz (peak velocity: 37 degrees /s). The gain change was 65% at 0.1 Hz and 60 degrees amplitude (peak velocity: 18 degrees /s), and 64% at 0.2 Hz and 60 degrees amplitude (peak velocity: 37 degrees /s). In the x1 adaptation experiment (30 degrees at 0.3 Hz), the percentage gain change was -62% under the same conditions, -50% at 0.1 Hz and 60 degrees amplitude, and -30% at 0.2 Hz and 60 degrees amplitude. No change of VOR gain was observed at other frequencies, and the subject was not adapted at 0.1 Hz and 30 degrees amplitude. The larger VOR gain increase in the x2 adaptation experiment for the faster head angular acceleration leads to the conclusion that the VOR gain mechanism can set vuite similar in terms of the head acceleration.

Adult↗
PubMed1996

Dermatologic nondisease.

Dermatologic nondisease is a relatively common problem presenting to dermatologists with rich symptomatology in important body image areas such as the face, scalp, and genital area. There is no objective dermatologic change present on examination. The most common psychiatric disease present is depression. Suicide is common, especially in women with perceived facial problems.

Body Image↗
PubMed1996

Body dysmorphic disorder.

Body dysmorphic disorder is one of the most difficult conditions to manage but a significant proportion of patients do respond to selective serotonin reuptake inhibitors. This group of drugs has helped to revolutionize the treatment of this common but disabling disorder of perceived body ugliness. The condition may affect up to 1% of the population in the United States. Patients often show obsessional features, and depression is common. Ever present is a risk of suicide in these patients.

Body Image↗
PubMed1996

The self-schema model: a theoretical approach to the self-concept in eating disorders.

Over the last several decades, the self-concept has been implicated as a important determinant of eating disorders (ED). Although considerable progress has been made, questions remain unanswered about the properties of self-concept that distinguish women with an ED from other populations, and mechanisms that link the self-concept to the disordered behaviors. Markus's self-schema model is presented as a theoretical approach to explore the role of the self-concept in ED. To show how the schema model can be integrated with existing work on the self-concept in ED, a framework is proposed that addresses the number, content, and accessibility of the self-schemas. More specifically, it is posited that a limited collection of positive self-schemas available in memory, in combination with a chronically and inflexibly accessible body-weight self-schema, lead to the disordered behaviors associated with anorexia nervosa and bulimia nervosa.

Adolescent↗