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PubMed1992

Flicker electroretinograms: a systems analytic approach.

We observed multiple maxima and minima in the electroretinogram (ERG) first harmonics which varied as a function of adaptation level, mean illuminance, and modulation depth. Based on differences in response characteristics we identified a minimum of 3 parallel mechanisms operating at 3 frequency regions within the ERG: a low frequency region (less than 10 Hz), a midfrequency region (centered near 20 Hz), and a high frequency region (centered near 40 Hz). The low frequency region was observed both in dark- and light-adapted conditions, was basically linear, and showed nonlinear behavior only at high contrasts in either light or dark adaptation. It may be modeled as a low pass filter. The midfrequency region was clearly observed only above cone threshold, was nonlinear at low contrasts, and may be modeled as a linear filter followed by an essential nonlinearity. The high frequency region was observed under high levels of light adaptation and also was nonlinear at low contrast. It may be modeled also as a linear filter followed by an essential nonlinearity.

Dark Adaptation↗

PubMed2003

Suprathreshold effects of adaptation produced by amplitude modulation.

This work extends the study of adaptation to amplitude modulation (AM) to the perception of highly detectable modulation. A fixed-level matching procedure was used to find perceptually equivalent modulation depths for 16-Hz modulation imposed on a 1-kHz standard and a 4-kHz comparison. The modulation depths in the two stimuli were compared before and after a 10-min exposure to a 1-kHz tone (adaptor) 100% modulated in amplitude at different rates. For modulation depths of 63% (20 log m = -4) and smaller, the perceived modulation depth was reduced after exposure to the adaptor that was modulated at the same rate as the standard. The size of this reduction expressed as a difference between the post- and pre-exposure AM depths was similar to the increase in AM-detection threshold observed after adaptation. Postexposure suprathreshold modulation depth was not appreciably reduced when the modulation depth of the standard was large (approached 100%). A much smaller or no reduction in the perceived modulation depth was also observed when the modulation rates of the adaptor and the standard tone were different. The tuning of the observed effect of the adaptor appears to be much sharper than the tuning shown by modulation-masking results.

Adaptation, Physiological↗

PubMed1983

Texture changes versus size changes as stimuli for motion in depth.

As an object approaches the eye, its retinal image size grows larger and its surface texture appears to grow coarser. We compare these two visual correlates of motion in their effectiveness as stimuli for motion in depth. In some experiments texture and object size both expanded or both contracted; in other experiments the two stimuli were pitted against each other. When texture and size change as for a rigid, nonrotating real world object an untextured square can be a more effective stimulus for motion in depth than the same square with texture. On way of describing this finding is to calculate the departure from linear summation of texture and size contributions. The departure is greatest when texture is static, being even greater than when texture changes in the opposite direction to size.

Adaptation, Ocular↗

PubMedDate not supplied

Direction repulsion in motion transparency.

A series of experiments investigated perceived direction of motion and depth segregation in motion transparency displays consisting of two planes of dots moving in different directions. Direction and depth judgments were obtained from human observers viewing these "bi-directional" animation sequences with and without explicit stereoscopic depth information. We found that (1) misperception of motion direction ("direction repulsion") occurs when two spatially intermingled directions of motion are within 60 deg of each other; (2) direction repulsion is minimal at cardinal directions; (3) perception of two directions of motion always results in separate motion planes segregated in depth; and (4) stereoscopic depth information has no effect on the magnitude of direction repulsion, but it does disambiguate the depth relations between motion directions. These results are developed within the context of a two-stage model of motion transparency. On this model, motion directions are registered within units subject to inhibitory interactions that cause direction repulsion, with the outputs of these units pooled within units selective for direction and disparity.

Adaptation, Ocular↗

PubMed2003

Psychosocial adaptation of immigrant Greek children from the former Soviet Union.

BACKGROUND: The objective of this study was to assess psychiatric disorders in, and the psychosocial adaptation and academic performance of, children of immigrant families of Greek origin from countries of the former Soviet Union. METHOD: At a preliminary stage, all immigrant children (276) aged 8-12 years attending 22 schools in a working-class suburb of Athens were assessed by their teachers in terms of behaviour and academic performance. They and their families had migrated to Greece within the previous three years. A matching control group of native children (251) attending the same schools and classes was also assessed. For an in-depth assessment of psychopathology and social adaptation, 65 immigrant and 41 native children were randomly selected from the two larger groups and were further assessed. RESULTS: No statistically significant differences were observed between the immigrant and native children in terms of psychopathology and social adaptation, although a few differences were observed in subscales. However, there were significant differences between the groups in academic performance, that of the immigrant group being poorer, particularly in language-related areas (p < 0.01). In the light of these results, language enrichment classes are suggested for immigrant children who need them.

Child↗

PubMed2004

Short-term adaptation of auditory receptive fields to dynamic stimuli.

Short-term adaptation and recovery from adaptation have a strong impact on the processing of dynamic stimuli. Adaptive effects on neuronal activity have been studied most commonly for changes in first-order statistics of stimuli such as stepwise increments or decrements in stimulus amplitude. However, changes in higher moment statistics, such as the variance of the amplitude distribution in visual stimuli, also can invoke pronounced adaptation behavior. We demonstrate here that neurons in the inferior colliculus (ICC) of the cat show adaptation to dynamic auditory stimuli that differ in the variance of their modulation depth distribution. In addition, it is shown that neurons show adaptation to other higher moment statistics (e.g., kurtosis) of the modulation envelope. The time course of adaptation is specific for the altered stimulus property and the direction of parameter change. The use of dynamic stimuli allows an estimate of the effects of the adaptation on the temporal response properties of the neurons. We demonstrate that temporal receptive fields of neurons undergo change during the course of adaptation. We show that adaptation to variance in the ICC has many similarities to that in the retina and suggest that adaptation to variance is a general property of sensory systems that allows them to effectively deal with a nonstationary environment.

Acoustic Stimulation↗

PubMed2005

Homography-based visual servo regulation of mobile robots.

A monocular camera-based vision system attached to a mobile robot (i.e., the camera-in-hand configuration) is considered in this paper. By comparing corresponding target points of an object from two different camera images, geometric relationships are exploited to derive a transformation that relates the actual position and orientation of the mobile robot to a reference position and orientation. This transformation is used to synthesize a rotation and translation error system from the current position and orientation to the fixed reference position and orientation. Lyapunov-based techniques are used to construct an adaptive estimate to compensate for a constant, unmeasurable depth parameter, and to prove asymptotic regulation of the mobile robot. The contribution of this paper is that Lyapunov techniques are exploited to craft an adaptive controller that enables mobile robot position and orientation regulation despite the lack of an object model and the lack of depth information. Experimental results are provided to illustrate the performance of the controller.

Algorithms↗

PubMed1987

Flicker adaptation in the peripheral retina.

With strict fixation, a flickering light spot smaller than 3 deg presented to the peripheral retina will rapidly appear to lose contrast and stop flickering within 35 s, before fading away completely. The time required for this adaptation to occur decreases with: decreasing depth of modulation (97-9%); decreasing stimulus diameter (2 deg-7 min arc); increasing retinal eccentricity (20-50 deg); and increasing flicker frequency (1-7 Hz). Interestingly, the effect does not depend upon the regularity of the flickering stimulus, and it occurs twice as fast for stimuli presented to the temporal retina as for stimuli presented to the nasal retina. When changes in retinal eccentricity are compensated for by taking into account the cortical magnification factor, the time needed for perceived flicker to disappear remains constant at all eccentricities. With dichoptic stimulation interocular transfer is about 35%, suggesting a cortical contribution to flicker adaptation. The results indicate that the visual system adapts rather easily to peripheral flickering stimuli. Similarities as well as differences to motion adaptation are discussed.

Adaptation, Ocular↗

PubMed1990

Adaptation to optically-increased interocular separation under naturalistic viewing conditions.

Mirror spectacles which enhance binocular disparity by optically doubling the normal separation between the eyes were used to create conditions of combined perceptual and oculomotor conflict. Apparent depth and distance, as well as tonic accommodation, tonic vergence, and accommodative-vergence gain (response AC/A ratio), were assessed immediately before and after a 30 min exposure period of naturalistic viewing with the spectacles. Wearing the spectacles produced an increase in tonic vergence, and perceptual aftereffects consisting of increased apparent distance and depth. The results indicate that oculomotor conflict associated with enhanced interocular separation may be resolved through adaptation of tonic vergence, rather than through alteration of accommodative-vergence gain. The results also demonstrate that perceptual conflict between disparity and multiple veridical depth cues does not necessarily produce adaptive modification of the relationship between binocular disparity and apparent depth.

Accommodation, Ocular↗

PubMed1994

A transparent motion aftereffect contingent on binocular disparity.

Under transparent motion conditions overlapping surfaces are perceived simultaneously, each with its own direction. The motion aftereffect (MAE) of transparent motion, however, is undirectional and its direction is opposite to that of a sensitivity-weighted vector sum of both inducing vectors. Here we report a bidirectional and transparent MAE contingent on binocular disparity. Depth (from retinal disparity) was introduced between two patterns. A fixation dot was presented at zero disparity, that is, located between the two adaptation patterns. After adaptation to such a stimulus configuration testing was carried out with two stationary test patterns at the same depths as the preceding moving patterns. For opposite directions a clear transparent MAE was perceived. However, if the adaptation directions were orthogonal the chance of a transparent MAE being perceived decreased substantially. This was subject dependent. Some subjects perceived an orthogonal transparent MAE whereas others saw the negative vector sum-an integrated MAE. In addition the behavior of the MAE when the distance in depth between adapting and test patterns was increased was investigated: it was found that the visibility of the MAE then decreased. Visibility is defined in this paper as: (i) the percentage of the trials in which MAEs are perceived and (ii) the average MAE duration. Both measures decreased with increasing distance. The results suggest that segregation and integration may be mediated by direction-tuned channels that interact with disparity-tuned channels.

Contrast Sensitivity↗

PubMed1984

Negative aftereffect arising from prolonged viewing of induced movement-in-depth.

Prolonged induced movement-in-depth in a static circle was elicited by a spiral stimulus. Afterwards an aftereffect was observed in the circle. The aftereffect was towards the subject after induced movement away from the subject, and away from the subject after induced movement towards the subject. Longer aftereffect was observed with a circle central to the inducing stimulus than with a circle peripheral to the inducing stimulus. In contrast to some other psychophysical effects, no clear-cut directional asymmetry was observed.

Adaptation, Ocular↗

PubMed2005

Motion in depth from interocular velocity differences revealed by differential motion aftereffect.

There are two possible binocular mechanisms for the detection of motion in depth. One is based on disparity changes over time and the other is based on interocular velocity differences. It has previously been shown that disparity changes over time can produce the perception of motion in depth. However, existing psychophysical and physiological data are inconclusive as to whether interocular velocity differences play a role in motion in depth perception. We studied this issue using the motion aftereffect, the illusory motion of static patterns that follows adaptation to real motion. We induced a differential motion aftereffect to the two eyes and then tested for motion in depth in a stationary random-dot pattern seen with both eyes. It has been shown previously that a differential translational motion aftereffect produces a strong perception of motion in depth. We show here that a rotational motion aftereffect inhibits this perception of motion in depth, even though a real rotation induces motion in depth. A non-horizontal translational motion aftereffect did not inhibit motion in depth. Together, our results strongly suggest that (1) pure interocular velocity differences can produce motion in depth, and (2) the illusory changes in position from the motion aftereffect are generated relatively late in the visual hierarchy, after binocular combination.

Adaptation, Psychological↗

PubMed2002

Context and the motion aftereffect: occlusion cues in the test pattern alter perceived direction.

A horizontally moving vertical grating viewed through a diamond-shaped aperture can be made to appear to move either upwards or downwards by introduction of appropriate depth-ordering cues at the boundaries of the aperture (Duncan et al. 2000 Journal of Neuroscience 20 5885-5897). The grating is perceived to move towards (and sliding under) occluding 'near' surfaces, and parallel to 'far' surfaces. Here we show that these depth-ordering cues affect the perceptual interpretation of the motion aftereffect (MAE) as well. After adaptation to unambiguous horizontal motion, the MAE direction deviates from horizontal towards near surfaces. However, the influence of depth-ordering cues on the illusory motion of the MAE is generally less than that seen for 'real' motion. Implications for theories of depth-motion and depth-MAE interactions are discussed.

Adaptation, Psychological↗

PubMed1995

[Ecology, adaptation and biorhythms].

The interfusion of environmentology and chronobiology makes it possible to explore various physiological mechanisms which arose in the process of evolution as a response to the external challenges. Therefore, a living organism adapts to a changing situation on the environmental and evolutional time scale. Since the temporal structure of environment is rhythmic by nature, body parameters may be strongly dependent on the environmental factors during adaptation. Results of the in-depth environmental and physiological studies of representatives of different climatic-geographical regions pointed to a series of common and individual properties of the human body reaction to an environment. The combination of hypoxia and hypercapnia (rebreathing test) brought into light a relationship of the reciprocal reaction of respiration and circulation to the body mass index and the average annual temperature in a region. The higher the temperature, the lower the body mass index, the weaker the hemodynamic reaction and the more expressed the ventilatory reaction.

Adaptation, Physiological↗

PubMed2000

Changes in stereoscopic depth perception caused by decentration of spectacle lenses.

The effect that decentered spectacle (ophthalmic) lenses exert on depth perception has been studied, evaluating stereopsis through the disparity range (maximum horizontal disparity) for random-dot stereograms (RDS). The results show that variations in fusional convergence due to increments of decentration can diminish the stereopsis in observers, reducing the region within which stereoscopic correspondence can take place. Decreases in disparity ranges were found for vertical and horizontal prismatic effects, although the prismatic effect necessary for this was less in the vertical case. A decreased disparity range has also been confirmed with figural-stimuli stereograms and using prisms for generating the prismatic effects.

Adaptation, Ocular↗

PubMed2003

Structure-based analysis of high pressure adaptation of alpha-actin.

Deep-sea fishes occur to depths of several thousand meters, and at these abyssal depths encounter pressures that shallower living fishes cannot tolerate. Tolerance of abyssal pressures by deep-sea fish is likely to depend in part on adaptive modifications of proteins. However, the types of structural modifications to proteins that allow function at high pressure have not been discovered. To elucidate the mechanisms of protein adaptation to high pressure, we cloned the alpha-skeletal actin cDNAs from two abyssal Coryphaenoides species, C. armatus and C. yaquinae, and identified three amino acid substitutions, V54A or L67P, Q137K, and A155S, that distinguish these abyssal actins from orthologs of alpha-actin from non-abyssal Coryphaenoides. These substitutions, Q137K and A155S, prevent the dissociation reactions of ATP and Ca2+ from being influenced by high pressure. In particular, the lysine residue at position 137 results in a much smaller apparent volume change in the Ca2+ dissociation reaction. The V54A or L67P substitution reduces the volume change associated with actin polymerization and has a role in maintaining the DNase I activity of actin at high pressure. Together, these results indicate that a few amino acid substitutions in key functional positions can adaptively alter the pressure sensitivity of a protein.

Actins↗

PubMed1995

An adaptable association between vertical and horizontal vergence.

Vertical phoria (vergence error under monocular viewing conditions) can be trained to vary with conjugate eye position. The adaptive response controls the vertical alignment of the two eyes in the absence of binocular disparity and is used to compensate for binocular changes of the oculomotor system induced by developmental and environmental factors. Vertical phoria was associated with horizontal disparity vergence by adapting vertical vergence to two vertically disparate targets separated along the depth axis. This association was primarily dependent on the horizontal vergence as opposed to monocular eye position or binocular conjugate eye position. Following this adapted association with horizontal disparity vergence, vertical phoria aftereffects were also evoked by accommodative vergence. Previous reports have demonstrated an adapted association between vertical phoria and conjugate eye position. The current report examines the difference in the vertical phoria resulting from adaptation to vertically disparate targets separated along either the vertical axis or depth axis. The amplitude of the vertical vergence aftereffect was approximately 4 times greater for targets separated along the depth axis than in the vertical meridian. The association between vertical phoria with conjugate eye position and horizontal vergence is proposed to result from a cross-coupling of vertical vergence with supranuclear regions that control conjugate and horizontal vergence eye movements. A selective interaction would enable the oculomotor system to correct disturbances in specific supranuclear regions as they interface with vertical vergence.

Accommodation, Ocular↗

PubMed2005

Gaze direction modulates visual aftereffects in depth and color.

Prior physiological studies indicate that gaze direction modulates the gain of neural responses to visual stimuli. Here, we test gaze modulation in the perceptual domain using color and depth aftereffects. After confirming retinotopy of the effects, we employed a balanced alternating adaptation paradigm (adaptation alternates between opponent stimuli) to demonstrate that opposite color and depth aftereffects can co-develop at the same retinal location for different gaze directions. The results provide strong evidence for (a) gaze modulation of aftereffects, (b) generality of gaze modulation across two visual attributes, and (c) perceptual correlates of the modulation of neural activity by gaze direction.

Color Perception↗