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PubMed1974

Interocular transfer of a visual after-effect in normal and stereoblind humans.

1. Following inspection of a high contrast grating a test grating of a slightly different orientation will briefly appear rotated from its true orientation in a direction opposite to that of the adapting grating.2. The extent of interocular transfer of this phenomenon (the tilt after-effect) was measured in a number of normal subjects and in four subjects (three of whom had a strabismus) who lacked stereopsis.3. In contrast to the normal subjects, none of the four stereoblind subjects showed any interocular transfer of the tilt after-effect. Amongst the normal subjects the extent of transfer of this after-effect was positively correlated with the subject's stereoacuity. Maximum transfer (70%) was found in the subject with the best stereoacuity. In many subjects transfer was greater from the dominant eye to the non-dominant eye than vice versa.4. By analogy with experiments on cats deprived of congruent visual input to the two eyes early in life it is argued that the stereoblind subjects lack any binocularly driven cortical neurones.

Adaptation, Ocular↗
PubMed1973

Haptic illusion: apparent elongation of a disk rotated between the fingers.

A disk (coin) turned end over end between thumb and forefinger feels longer to the turning hand. The illusion grows rapidly for 30 seconds but does not become asymptotic within 60 seconds. The illusion increases with coin size and turning rate, and is independent of holding pressure. It appears to involve illusory mechanisms in both hands.

Figural Aftereffect↗
PubMed1972

Average evoked responses and psychophysical performance in patients with pseudohypoparathyroidism.

Perceptual function in eight patients with pseudohypoparathyroidism (PHP) was studied with two neurophysiological measures, the average evoked response (AER) and nerve conduction velocity. A battery of psychophysical tasks including reaction time, size estimation, `hidden pictures,' and the rod and frame procedure was also used. Patients with PHP had significantly longer latency visual AER and slower reaction time than a group of normal volunteers, and they performed erratically and poorly on the other psychophysical tasks. Differentiating these patients with diffuse mental deficiency were two relatively specific perceptual response patterns: (1) AER amplitude decreased with increasing stimulus intensity, and (2) reaction time was abnormally influenced by the duration of the preparatory interval. Both of these patterns have previously been found in other patient groups.

Adolescent↗
PubMed1969

Perception.

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Body Image↗
PubMed1971

Perception.

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Afterimage↗
PubMed1975

Perception.

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Adaptation, Ocular↗
PubMedDate not supplied

Effect of aging on visual shape distortion.

BACKGROUND: Individuals experience a visual illusion created by shape interaction: when two shapes are presented successively and briefly, the form of the second (test) shape appears distorted due to the form of the first (prime) shape; this shape interaction is called the shape distortion effect. While age-related deterioration in performance is found in various aspects of visual perception, the effect of aging on the shape distortion effect has not been evaluated. OBJECTIVE: The purpose of this study is to determine the effect of aging on the shape distortion effect. METHODS: We measured the perception of briefly presented elementary shapes and of the shape distortion effect in 29 healthy volunteers, with ages ranging from 18 to 83 years. For each shape interaction trial, a prime rectangle was presented (vertical or horizontal) for 45 ms, followed by an interstimulus interval for 135 ms, a test circle for 60 ms and finally a random dot mask for 300 ms. The test circle was presented in each quadrant of the visual field. The prime rectangle was flashed either at the same position as the test circle (0 degrees offset, intrahemifield) or 11 degrees apart, displaced horizontally in the opposite hemifield (11 degrees offset, interhemifield). In the elementary-shape trials, there was no prime, and the test shape was a circle or an ellipse. Using the method of adjustment, the percent elongation [(longer diameter - shorter diameter)/(shorter diameter) x100] of the reproduced ellipse was computed. RESULTS: The mean percent elongation in response to the elementary shapes did not vary with increasing age. The shape distortion effect decreased significantly with increasing age during both intra- and interhemifield conditions. The mean shape distortion effect was larger for the intrahemifield condition than for the interhemifield one. CONCLUSION: The shape distortion effect decreases with advancing age while the perception of elementary shapes does not. These results indicate a severer age-related dysfunction of the cerebral processing of shape interaction than that of elementary-shape perception.

Adult↗
PubMed1991

Neuronal motion after-response induced in the tectal neurons of toads by moving textured background.

When an object is held stationary in the center of the receptive field of a tectal neuron in a toad and a textured background is moved for a period of time, some neurons produce a burst of discharges immediately after the movement of the background ceases. This effect was first found in a recent study and temporarily called 'neuronal motion after-response'. A total of 66 tectal neurons in toads were examined, and 29 out of them showed the effect. In the different neurons under investigation, the firing rate varied from a few spikes to discharges of very long duration. The appearance of the motion after-response was independent of either the object/background contrast (i.e. black against white vs. white against black) or the direction of the background movement. In order to induce this effect, however, the object must be of sufficient size, and the background must be moved for a sufficient length of time. For most tectal neurons, an 8 x 8 degree square was large enough to induce the motion after-response, but for several others, the size of the object had to be similar to that of the excitatory receptive field of the neuron. The duration of the background movement was also crucial: at least 20 s of background movement was necessary for the motion after-response to occur.

Animals↗
PubMed1993

Chronic palinopsia in schizophrenia.

Palinopsia seems to be a very rare phenomenon in functional psychotic disorders. In this paper, we report on a patient with chronic schizophrenia who displayed chronic persisting palinopsia embedded in a plethora of rare mental phenomena. The possible theoretical relevance of this observation is discussed.

Adult↗
PubMed2006

A single system explains human speed perception.

Motion is fully described by a direction and a speed. The processing of direction information by the visual system has been extensively studied; much less is known, however, about the processing of speed. Although it is generally accepted that the direction of motion is processed by a single motion system, no such consensus exists for speed. Psychophysical data from humans suggest two separate systems processing luminance-based fast and slow speeds, whereas neurophysiological recordings in monkeys generally show continuous speed representation, hinting at a single system. Although the neurophysiological findings hint at a single system, they remain inconclusive as only a limited amount of cells can be measured per study and, possibly, the putative different motion systems are anatomically separate. In three psychophysical motion adaptation experiments, we show that predictions on the basis of the two-motion system hypothesis are not met. Instead, concurrent modeling showed that both here-presented and previous data are consistent with a single system subserving human speed perception. These findings have important implications for computational models of motion processing and the low-level organization of the process.

Adaptation, Physiological↗
PubMed2000

Perceived motion in complementary afterimages: verification of a neural network theory.

Steady fixation of a regular pattern like a bar grating or concentric circles leads to a complementary afterimage at pattern offset. The afterimage has the appearance of shimmering lines that are locally orthogonal to the orientations of the inducing image. Additionally, the afterimage includes motion running parallel to the orientation of the afterimage lines. We argue that this afterimage motion supports the existence of a cue to motion that is based on the spatial organization of oriented responses. This cue was previously proposed after analysis of a neural network model of visual perception. We test predictions of the model on various types of complementary afterimage inducing stimuli. When a contrast or size gradient is included in the inducing image, the afterimage motion moves toward the higher part of the gradient, in agreement with the model. Implications of this cue for computational and neurophysiological theories of motion perception are discussed.

Figural Aftereffect↗
PubMed2005

Transfer of tilt after-effects between second-order cues.

Second-order cues are visual stimuli that are detectable by human observers, without eliciting a peak in Fourier energy that corresponds to their perceptual properties. The most commonly studied exemplars of second-order cues are those defined by modulation of local contrast (CM). It is widely accepted that such cues are initially detected separately from first-order, luminance modulated (LM), cues. However, after-effects have been shown to transfer between first- and second-order cues (LM and CM, respectively). This suggests the existence of a late link in the mechanisms that subserve their processing. To extend the investigation of the mechanisms for processing second-order cues we consider cues defined by modulations in local orientation (OM). Using a tilt-after-effect (TAE) paradigm, we found partial transfer of adaptation between LM and OM cues, confirming the presence of a link between first and second-order cues. Furthermore, we found a partial transfer of TAE between OM and CM cues. These results suggest that, at or before the site of adaptation, information from all visual cues is combined. However, as transfer of adaptation is below 100% in all cases, this is only a partial integration of information.

Adaptation, Ocular↗
PubMed1989

On the evidence for a 'pure' binocular process in human vision.

Wolfe (1986, Psychol. Rev. 93, 269-282) proposed a model of human binocular vision based on the assumption of two functionally distinct classes of binocular neuron. These neurons may be regarded as logical AND and OR gates. In the present paper we assess the evidence relevant to this assumption. We find that while both types of binocular neuron have been described in the cortex of cat and monkey, there is no indication that they form functionally separate populations. Critical analysis of the psychophysical evidence for AND and OR channels in human vision suggests that much of the data presented in favor of an AND channel is subject to alternative interpretations. We conclude that the available data are not consistent with the existence of separate channels as proposed by Wolfe.

Adaptation, Ocular↗
PubMed2002

Subjective color from apparent motion.

In an effect we call color from motion (CFM), apparent motion is accompanied by subjective color spread seen in physically achromatic regions. Here we report that physical lights can cancel the subjective color seen in CFM. As measured by cancellation, the saturation of the subjective color spread increases as the luminance of the test elements increase. Without luminance differences between test and surround elements, chromaticity differences alone can result in the perception of subjective color spread. In this case, subjective color spread is seen without seeing a subjective contour, suggesting that CFM does not require contour formation and that color - independent of contour - can be recovered in tandem with seeing motion. There are two modes in which CFM is perceived, either (1) as a localized change of illumination, a colored spotlight or shadow, moving over a textured surface or (2) as a moving, colored object seen through holes in an occluding surface. The mode in which CFM is seen depends on figural cues and on regional differences in luminance contrast between the chromatic elements and the achromatic background. Regions with distinct figural cues are always seen as moving; and CFM is seen in the first mode if the regions are of lower luminance contrast and in the second mode if the regions are of higher luminance contrast. Without figural cues, the regions of lower luminance contrast are always seen to move and CFM is seen in the first mode.

Color Perception↗
PubMed1989

Visual persistence and adult dyslexia.

Visual persistence was investigated in adults with and without dyslexia in order to determine whether the adults with dyslexia demonstrate problems similar to those found in childhood dyslexia. Using a temporal separation threshold measure and procedures derived from signal detection theory, sensitivity to sequentially presented form information was determined for the two types of adults. The results showed that the sensitivity of the adults with dyslexia was impaired relative to that of the nondisabled adults when parts of a test stimulus were presented to adjacent retinal areas. This result suggests that, under certain conditions, visual persistence is longer for adults with dyslexia. The results are discussed within the context of a recent theory of dyslexia (Lovegrove, Martin & Slaghuis, 1986) that incorporates the operation of sustained and transient visual mechanisms.

Adolescent↗