Dual adaptation and adaptive generalization of the human vestibulo-ocular reflex

In two experiments, we examined the possibility that the human vestibulo-ocular reflex (VOR) is subject todual adaptation (the ability to adapt to a sensory rearrangement more rapidly and/or more completely after repeated experience with it) andadaptive generalization (the ability to adapt more readily to a novel sensory rearrangement as a result of prior dual adaptation training). In Experiment 1, the subjects actively turned the head during alternating exposure to a visual-vestibular rearrangement (target/head gain=0.5) and the normal situation (target/head gain=0.0). These conditions produced both adaptation and dual adaptation of the VOR but no evidence of adaptive generalization when tested with a target/head gain of 1.0. Experiment 2, in which exposure to the 0.5 gain entailed externally controlled (i.e., passive) whole body rotation, resulted in VOR adaptation but no dual adaptation. As in Experiment 1, no evidence of adaptive generalization was found.     

Factors affecting proprioceptive adaptation to prismatic displacement

Two prism displacement experiments were conducted to determine the effects of reducing proprioceptive feedback on resultant adaptation magnitude. In Experiment 1, proprioceptive reduction was produced by requesting subjects to employ passive Ivs. active) and/or fast- Ivs. slow-) paced arm movement during prism exposure. When both of these conditions were present, a significant reduction in the magnitude of proprioceptive adaptation and a significant increase in the magnitude of visual adaptation were produced. In Experiment 2, hypnotic anesthesia was employed to reduce felt sensation in an adapting limb during a prism displacement situation. This manipulation reduced proprioceptive adaptation to a nonsignificant level. The combined results of the two experiments reveal several conditions that can serve to reduce proprioceptive adaptation during prism displacement.     

Proprioception and the production of adaptation and intermanual transfer to prismatic displacement

Proprioceptive adaptation to prismatic displacement and resultant intermanual transfer were investigated in two experiments. In Experiment 1, magnitude of adaptation and transfer were assessed as a result of the reduction of felt sensation via hypnotic anesthesia in an adapting limb. Such anesthesia reduced the magnitude of adaptation in that limb and resultant transfer in the nonadapting limb to a nonsignificant level. Such was not the case when the adapting limb was nonanesthetic. In Experiment 2, adaptation and transfer magnitude were assessed as the result of anesthetic induction in a nonadapting limb. When this was the case, adaptation was produced in the adapting limb but not in the anesthetized, nonadapting limb. The results of the two experiments generally point to proprioception as being the major source of input to the production of intermanual transfer in a prismatic adaptation task.     

Evidence for a common motion mechanism of luminance-modulated and contrast-modulated patterns: selective adaptation.

Selective adaptation effects were measured with contrast-modulated patterns and sine-wave gratings in order to determine the extent to which the two patterns are processed by common mechanisms. Direction-specific adaptation effects were measured for a contrast-modulated adapting pattern and a test pattern. The contrast-modulated adapting pattern was composed of a sine-wave grating of 8 cycles deg-1 whose contrast was spatially modulated by a sinusoid of 1 cycle deg-1 at one of four levels: 100%, 60%, 30%, or 0%. The results showed that contrast-modulation thresholds for contrast-modulated gratings were raised by 0.3 to 0.5 log units following adaptation to a contrast-modulated grating moving in the same direction as the test pattern, relative to thresholds obtained following adaptation to a contrast-modulated grafting moving in the opposite direction. Cross-adaptation effects were also measured with a sine-wave adapting pattern and a contrast-modulated test pattern. The sine-wave adapting pattern was a sine-wave grating of 1 cycle deg-1 whose contrast was set to one of three levels: 16.4%, 1.25%, or 0%. The contrast-modulated test pattern was a sine-wave grating of 8 cycles deg-1 whose contrast was modulated by a sinusoid of 1 cycle deg-1. The results revealed that contrast-modulation thresholds for contrast-modulated gratings were raised by approximately 0.25 log units following adaptation to moving sine-wave gratings, relative to thresholds obtained following adaptation to a uniform field. Cross-adaptation effects were also obtained with a contrast-modulated adapting pattern and a sine-wave test pattern. The results support the view that signals generated from luminance-domain stimuli and from contrast-domain stimuli are processed by a common motion mechanism.     

Response organization in selective adaptation to speech sounds

Previous experiments in speech perception using the selective adaptation procedure have found a shift in the locus of the category boundary for a series of speech stimuli following repeated exposure to an adapting syllable. The locus of the boundary moves toward the category of the adapting syllable. Most investigators have interpreted these findings in terms of feature detector models in which specific detectors are reduced in sensitivity through repeated adaptation. The present experiment was conducted to determine whether the adaptation results might be due to changes in response organization as a consequence of the labeling instructions presented to subjects in selective adaptation experiments. A perceptually ambiguous speech stimulus was selected from the middle of a [bi]-[di] test series and used as an adaptor under two different sets of instructions. One group of subjects was told that the adapting stimulus was the syllable [bi], while another group was told that the stimulus was the syllable [di]. The acoustically ambiguous adaptor failed to produce a shift in the locus of the category boundary in the direction predicted on the basis of the labeling instructions presented to subjects. These results indicate that the acoustic attributes and perceived quality of the adapting stimulus determine the direction and magnitude of the adaptation effects rather than the labels provided by the experimenter.     

Reduced felt arm sensation effects on visual adaptation

Proprioception is often considered to be critically involved in producing adaptation to a prism-induced visual displacement. The present study focused on reduction of proprioceptive feedback during prism exposure by means of hypnotically induced anesthesia in the adapting arm. In addition, intermanual transfer was considered. Results showed adaptation occurring in situations where S could feel arm sensations while viewing arm movement during a prism exposure. However, if the adapting arm was hypnotically anesthetized while still remaining mobile, adaptation did not occur. No intermanual transfer was found between the adapted arm and the unadapted arm.     

Adaptation of the two arms to opposite prism displacements

In normal subjects, the two arms were exposed separately to prismatic displacements of opposite sign, using the eye ipsilateral to the exposed arm. Opposite adaptive shifts were induced on each arm whether the eye ipsilateral to the arm (i.e. exposed to a displacement of the same sign as the arm) or the eye controlateral to the arm (i.e. exposed to a displacement of opposite sign) was used during testing. This result precludes the possible role of oculomotor signals in this type of prism adaptation.     

Aging affects acquisition and reversal of reward-based associative learning

Reward-based associative learning is mediated by a distributed network of brain regions that are dependent on the dopaminergic system. Age-related changes in key regions of this system, the striatum and the prefrontal cortex, may adversely affect the ability to use reward information for the guidance of behavior. The present study investigated the effects of healthy aging on different components of reward learning, such as acquisition, reversal, effects of reward magnitude, and transfer of learning. A group of 30 young (mean age = 24.2 yr) and a group of 30 older subjects (mean age = 64.1 yr) completed two probabilistic reward-based stimulus association learning tasks. Older subjects showed poorer overall acquisition and impaired reversal learning, as well as deficits in transfer learning. When only those subjects who showed evidence of significant learning were considered, younger subjects showed equivalently fast learning irrespective of reward magnitude, while learning curves in older subjects were steeper for high compared to low reward magnitudes. Acquired equivalence learning, which requires generalization across stimuli and transfer of learned contingencies to new stimuli, was mildly impaired in older subjects.     

Orientation-selective adaptation to crowded illusory lines

Visual adaptation has been successfully used as a psychophysical tool for studying the functional organisation of visual awareness. It has been shown that orientation-selective adaptation to a grating pattern occurs in crowded conditions. In such conditions, simultaneous presentation of flanking distractors pushes the target stimulus out of conscious perception and severely impairs orientation discrimination in the periphery of the visual field. In the present study, orientation-selective adaptation to illusory lines induced by two line gratings abutting each other with a phase shift was examined in crowded and non-crowded conditions. To rule out the effects of lower level adaptations we used an animation paradigm in which the orientations of the two line gratings were altered repeatedly during adaptation phase without any change in the orientation of the resulting illusory line. Although performance of subjects in reporting the orientation of crowded illusory lines was at chance level, orientation-selective adaptation was preserved for crowded as well as non-crowded adapting targets. Two control experiments demonstrated that adaptation to endpoints of real lines at the location of abutting grating lines had minimal effect on the adaptation to illusory lines; and changes in the configuration of endpoints could not be responsible for better performance when adapting and test stimuli were different. We conclude that a crowding effect occurs after illusory lines have been processed in the visual stream. Since illusory lines seem to be represented at relatively early stages of visual processing (e.g. area V2), adaptation to crowded illusory stimuli suggests that neuronal activation in those early stages is not necessarily correlated with conscious perception.     

View-specific coding of face shape

Monkey and human cortex contain view-specific face neurons, but it remains unclear whether they code face shape. We tested the view specificity of face-shape coding by inducing figural face aftereffects at one viewpoint (3/4 left) and testing generalization to different viewpoints (front view and 3/4 right). The aftereffects were induced by adaptation to consistent figural distortions (contracted or expanded), which shifts the distortion perceived as most normal toward the adapting distortion. The strong aftereffect that was observed at the adapting view was significantly and substantially reduced for both front-view test faces and mirror-image (3/4 right) test faces, indicating view specificity. The limited transfer across mirror views is strong evidence of view specificity, given their figural similarity. The aftereffects survived a size change between adaptation and test faces (Experiment 2), a result that rules out low-level adaptation as an explanation. These results provide strong evidence that face-shape coding is view-specific.     

“Extinction” of the McCollough effect does not transfer interocularly

A McCollough effect was induced in subjects by having them view typical adapting stimuli binocularly for 5 min. In the control condition, the strength of the McCollough effect was measured 20 min after the end of the adaptation. The strength was measured during monocular and binocular viewing of a test pattern via a color cancellation technique. Monocular strengths for the two eyes of a given subject were equal to each other and slightly weaker than the binocular strength. In the test condition, 15 min of the 20 min between adaptation and testing were spent monocularly viewing black and white gratings of the same orientation and spatial frequency as the adapting gratings. The strength of the effect as measured ipsilaterally was markedly decreased from that in the control condition. The strength of the effect as measured with the contralateral eye showed only a small decrease from that of the control condition. This finding is relevant to various models of the McCollough effect and related color aftereffects, especially those that posit a “learning” type of mechanism between achromatic spatial channels (which exhibit clear interocular transfer of various achromatic effects) and monocular color channels.     

Prism Adaptation and Aftereffect: Specifying the Properties of a Procedural Memory System

Prism adaptation, a form of procedural learning, is a phenomenon in which the motor system adapts to new visuospatial coordinates imposed by prisms that displace the visual field. Once the prisms are withdrawn, the degree and strength of the adaptation can be measured by the spatial deviation of the motor actions in the direction opposite to the visual displacement imposed by the prisms, a phenomenon known as aftereffect. This study was designed to define the variables that affect the acquisition and retention of the aftereffect. Subjects were required to throw balls to a target in front of them before, during, and after lateral displacement of the visual field with prismatic spectacles. The diopters of the prisms and the number of throws were varied among different groups of subjects. The results show that the adaptation process is dependent on the number of interactions between the visual and motor system, and not on the time spent wearing the prisms. The results also show that the magnitude of the aftereffect is highly correlated with the magnitude of the adaptation, regardless of the diopters of the prisms or the number of throws. Finally, the results suggest that persistence of the aftereffect depends on the number of throws after the adaptation is complete. On the basis of these results, we propose that the system underlying this kind of learning stores at least two different parameters, the contents (measured as the magnitude of displacement) and the persistence (measured as the number of throws to return to the baseline) of the learned information.     

Adaptation level as an explanation of the peak shift in generalization with movement stimuli

Two experiments examine the value of adaptation level theory as an explanation of the peak shift phenomenon in stimulus generalization using linear arm movements. The first experiment manipulates the differences in adaptation levels during training by varying the frequency of experience of the training stimulus. Significant shifts in the peaks of generalization gradients were subsequently identified. The peak shifts were in the direction predicted by adaptation level theory. The second experiment manipulates testing adaptation levels by biasing the generalization test movements. Three groups of subjects performed differentially weighted test sequences in which the relative number of short, medium, or long movements was manipulated. Significant peak shifts of generalization gradients were observed in the direction predicted by adaptation level theory.     

Adaptation Level as an Explanation of the Peak Shift in Generalization with Movement Stimuli

Two experiments examine the value of adaptation level theory as an explanation of the peak shift phenomenon in stimulus generalization using linear arm movements. The first experiment manipulates the differences in adaptation levels during training by varying the frequency of experience of the training stimulus. Significant shifts in the peaks of generalization gradients were subsequently identified. The peak shifts were in the direction predicted by adaptation level theory. The second experiment manipulates testing adaptation levels by biasing the generalization test movements. Three groups of subjects performed differentially weighted test sequences in which the relative number of short, medium, or long movements was manipulated. Significant peak shifts of generalization gradients were observed in the direction predicted by adaptation level theory.     

An adaptive network model covering metacognition to control adaptation for multiple mental models

Learning processes can be described by adaptive mental (or neural) network models. If metacognition is used to regulate learning, the adaptation of the mental network becomes itself adaptive as well: second-order adaptation. In this paper, a second-order adaptive mental network model is introduced for metacognitive regulation of learning processes. The focus is on the role of multiple internal mental models, in particular, the case of visualisation to support learning of numerical or symbolic skills. The second-order adaptive network model is illustrated by a case scenario for the role of visualisation to support learning multiplication at the primary school.     

Generalization hypothesis of abstract-concept learning: learning strategies and related issues in Macaca mulatta, Cebus apella, and Columba livia

The generalization hypothesis of abstract-concept learning was tested with a meta-analysis of rhesus monkeys (Macaca mulatta), capuchin monkeys (Cebus apella), and pigeons (Columba livia) learning a same/different (S/D) task with expanding training sets. The generalization hypothesis states that as the number of training items increases, generalization from the training pairs will increase and could explain the subjects' accurate novel-stimulus transfer. By contrast, concept learning is learning the relationship between each pair of items; with more training items subjects learn more exemplars of the rule and transfer better. Having to learn the stimulus pairs (the generalization hypothesis) would require more training as the set size increases, whereas learning the concept might require less training because subjects would be learning an abstract rule. The results strongly support concept or rule learning despite severely relaxing the generalization-hypothesis parameters. Thus, generalization was not a factor in the transfer from these experiments, adding to the evidence that these subjects were learning the S/D abstract concept.     

Contrast adaptation implies two spatiotemporal channels but three adapting processes

The contrast gain control model of adaptation predicts that the effects of contrast adaptation correlate with contrast sensitivity. This article reports that the effects of high contrast spatiotemporal adaptors are maximum when adapting around 19 Hz, which is a factor of two or more greater than the peak in contrast sensitivity. To explain the discrepancy, the predictions made by parallel versus cascaded models of spatiotemporal processing are compared. It is demonstrated that a parallel two-temporal channel model, in which the adaptive attenuation of a channel is proportional to its response, cannot explain the effects of adaptation on threshold contrast but that a cascaded model can. The cascaded model suggests that the visual system temporally encodes spatiotemporal signals via an adaptive transient encoding process that lies in cascade with an adaptable two-temporal channel system of sustained versus transient processes.     

Feature analyzers for the phonetic dimensionstop vs. continuant

Perception of sounds along the phonetic dimensionstop vs. continuant was studied by means of a selective adaptation procedure. Subjects first identified a series of synthetic consonant-vowel syllables whose formant transitions varied in duration, slope, and amplitude characteristics. They were perceived as either [ba] or [wa]. After the initial identification test, an adapting stimulus was presented repeatedly, and then the subjects again identified the original test series. Adapting with a stop (either [ba] or [da]) led to a decrease in the number of test stimuli identified as [ba], whereas adapting with the continuant sound [wa] led to an increase in the number of [ba] identification responses. Removing the vowel portion of an adapting stimulus greatly reduced the identification shift only when the resulting stimulus was no longer perceived as speech-like. A reduction in the number of [ba] identifications occurred even when a nonspeech “stop” (the sound of a plucked string) was used as the adapting stimulus, suggesting that phonetic processing is not a necessary condition for an adaptation effect.     

Stimulus generalization in two associative learning processes

Recent studies involving nonlinear discrimination problems suggest that stimuli in human associative learning are represented configurally with narrow generalization, such that presentation of stimuli that are even slightly dissimilar to stored configurations weakly activate these configurations. The authors note that another well-known set of findings in human associative learning, cue-interaction phenomena, suggest relatively broad generalization. Three experiments show that current models of human associative learning, which try to model both nonlinear discrimination and cue interaction as the result of 1 process, fail because they cannot simultaneously account for narrow and broad generalization. Results suggest that human associative learning involves (a) an exemplar-based process with configural stimulus representation and narrow generalization and (b) an adaptive learning process characterized by broad generalization and cue interaction.     

"Perception" versus "Learning": The effect of different instructions upon the central tendency shift

Abstract.— Earlier studies of context effects in stimulus generalization, especially in the adaption-level tradition, have failed to take into account the subjective difference between a learning experiment and an experiment in perception. In the present study, 68 student subjects were trained to discriminate a 30 cm vertical line from shorter and longer lines, and were subsequently tested for generalization with asymmetrical test series (centering around 34 cm). Half of the subjects were told that they were participating in a perception experiment, the other half that they were participating in a learning experiment. Subjects in the latter condition were considerably more influenced by context and gave a greater number of equivalence responses than did the subjects in the perception condition. Amount of training and discriminability of training stimuli did also influence the central tendency shift, but to a lesser extent.