Adaptation Aftereffects Research Articles

Prism adaptation aftereffects in stroke patients with spatial neglect: Pathological effects on subjective straight ahead but not visual open-loop pointing

Prism adaptation to rightward optical shifts during visually guided pointing is considered a promising intervention in right-hemisphere stroke patients with left spatial neglect. Conventionally, prism adaptation is assessed via aftereffects, on subjective straight ahead (SSA) pointing with eyes closed; or by visual open-loop pointing (VOL), i.e. pointing to a visual target without seeing the hand. Previous data suggest indirectly that prism aftereffects in neglect patients may be larger (pathologically so) when assessed by SSA than by VOL. But these measures have never been directly compared within the same patients after identical prism exposure. Accordingly we implemented both measures here within the same group of 13 neglect patients and 13 controls. Prism aftereffects were much larger for SSA than VOL in neglect patients, falling outside the normative range only for SSA. This may arise because the SSA task can itself involve aspects of neglect that may be ameliorated by the prism intervention, hence showing abnormal changes after prisms. The extent of SSA change after prisms varied between patients, and correlated with improvements on a standard cancellation measure for neglect. The lesions of patients who did versus did not show neglect improvement immediately after prisms provide an initial indication that lack of improvement may potentially relate to cortical damage in right intraparietal sulcus and white matter damage in inferior parietal lobe and middle frontal gyrus. Future studies of possible rehabilitative impact from prisms upon neglect may need to consider carefully how to measure prism adaptation per se, separately from any impact of such adaptation upon manifestations of neglect.

Factors contributing to the adaptation aftereffects of facial expression

Previous studies have demonstrated the existence of adaptation aftereffects for facial expressions. Here we investigated which aspects of facial stimuli contribute to these aftereffects. In Experiment 1, we examined the role of local adaptation to image elements such as curvature, shape and orientation, independent of expression, by using hybrid faces constructed from either the same or opposing expressions. While hybrid faces made with consistent expressions generated aftereffects as large as those with normal faces, there were no aftereffects from hybrid faces made from different expressions, despite the fact that these contained the same local image elements. In Experiment 2, we examined the role of facial features independent of the normal face configuration by contrasting adaptation with whole faces to adaptation with scrambled faces. We found that scrambled faces also generated significant aftereffects, indicating that expressive features without a normal facial configuration could generate expression aftereffects. In Experiment 3, we examined the role of facial configuration by using schematic faces made from line elements that in isolation do not carry expression-related information (e.g. curved segments and straight lines) but that convey an expression when arranged in a normal facial configuration. We obtained a significant aftereffect for facial configurations but not scrambled configurations of these line elements. We conclude that facial expression aftereffects are not due to local adaptation to image elements but due to high-level adaptation of neural representations that involve both facial features and facial configuration.

Asymmetrical after-effects of prism adaptation during goal oriented locomotion

In healthy subjects, sensorimotor after-effects of prism adaptation are known to be symmetric (they appear after using leftward and rightward optical deviations), whereas cognitive after-effects are asymmetric (they appear after using a leftward optical deviation) and rightward oriented. Sensorimotor and cognitive after-effects have been classically studied using different specific tasks. The purpose of the current study was to investigate whether both after-effects may be involved in a same visuo-spatial task. Therefore we compared the amplitude of after-effects following adaptation to a rightward or leftward optical deviation. After-effects were assessed by manual pointing or goal oriented locomotor task. The main result showed a greater amplitude for rightward locomotor after-effects (after adaptation to a leftward deviation) than for leftward locomotor after-effects (after adaptation to a rightward deviation). This means that cognitive after-effects may add to sensorimotor after-effects following adaptation to a leftward optical deviation. This asymmetry challenges the classical distinction between sensorimotor and cognitive after-effects of prism adaptation. Implications for the functional mechanisms and the neuroanatomical substrate of prism adaptation are discussed.

Effects of adaptation to Glass pattern structure and to path of optic flow

The effects of adaptation to radial and rotational polar optic flow on the classification of noisy test patterns are shown to be very similar to the effects of adaptation to polar Glass patterns on the classification of noisy Glass patterns (Clifford, C. W. G. & Weston, E. (2005). Aftereffect of adaptation to Glass patterns. Vision Research, 45 1355–1363.). In both cases there is a large shift in the signal strength at which test patterns are classified as radial or rotational with equal probability. Two asymmetries were discovered: (1) adaptation to optic flow alters the classification of Glass patterns, but the reverse is not true; and (2) adaptation to Glass patterns decreases detectability of patterns of the same type, but adaptation to optic flow has little effect on the detectability of patterns of any type. We conclude that the mechanisms that detect radial and rotational Glass patterns are independent and independently adaptable, but that the mechanisms that detect the path of optic flow, when directional effects are cancelled out, are linked in an opponent, push–pull fashion.

Aftereffect of contrast adaptation to a chromatic notched-noise stimulus

One of the most challenging topics in the study of human color vision is the investigation of the number of hue-selective channels that are necessary for the representation of color appearance at the post-opponent level and the bandwidth of their sensitivity. The present study aims to elucidate this issue by using a chromatic version of the notch-filtered noise (herein, notched-noise) stimulus for contrast adaptation. After adaptation to this stimulus, some color-sensitive mechanisms that selectively respond to missing hues in the notched-noise stimulus may remain sensitive, while the other mechanisms may be desensitized. The shifts in the color appearance of a gray test field after the adaptation to such a notched noise were measured using the method of adjustment. The results showed systematic shifts in the hue and saturation. They showed neither point nor line symmetric profiles with respect to the achromatic point in an isoluminant plane. The fittings of the results, obtained by using a tiny numerical model for assessing the hue-selective mechanisms, suggested that there are at least two narrowly tuned and at least three broadly tuned mechanisms. The narrowly tuned mechanisms are the most sensitive along the blue and yellow directions. The present study confirmed the variation of multiple channels at the post-opponent level and suggested that this variation may be responsible for the processing of color appearance.

Face adaptation aftereffects reveal anterior medial temporal cortex role in high level category representation

Previous studies have shown reductions of the functional magnetic resonance imaging (fMRI) signal in response to repetition of specific visual stimuli. We examined how adaptation affects the neural responses associated with categorization behavior, using face adaptation aftereffects. Adaptation to a given facial category biases categorization towards non-adapted facial categories in response to presentation of ambiguous morphs. We explored a hypothesis, posed by recent psychophysical studies, that these adaptation-induced categorizations are mediated by activity in relatively advanced stages within the occipitotemporal visual processing stream. Replicating these studies, we find that adaptation to a facial expression heightens perception of non-adapted expressions. Using comparable behavioral methods, we also show that adaptation to a specific identity heightens perception of a second identity in morph faces. We show both expression and identity effects to be associated with heightened anterior medial temporal lobe activity, specifically when perceiving the non-adapted category. These regions, incorporating bilateral anterior ventral rhinal cortices, perirhinal cortex and left anterior hippocampus are regions previously implicated in high-level visual perception. These categorization effects were not evident in fusiform or occipital gyri, although activity in these regions was reduced to repeated faces. The findings suggest that adaptation-induced perception is mediated by activity in regions downstream to those showing reductions due to stimulus repetition.

Spatial generalization in short-term perceptual adaptation to novel auditory spaces

Previous work shows that humans can rapidly adapt to novel mappings between auditory spatial cues and exocentric location and localize accurately with the novel mapping. Here, experiments using (1) a rotation and (2) a linear magnification of auditory space examined generalization of spatial adaptation to untrained or neglected regions of space. Individual head-related transfer functions (HRTFs) were used to simulate different source locations using headphones. Each experimental session was broken into three blocks: initial normal cues (measuring baseline performance), altered cues (showing adaptation), and final normal cues (measuring an adaptation aftereffect). In the altered cues trials, a source at X degrees was simulated using HRTFs that normally correspond to a source at (1) X+30 deg (rotation) or (2) 2X deg (linear magnification). After obtaining subjects’ localization responses to the sound stimulus, feedback was given using a light-emitting diode located at the correct position (X deg). Results of these experiments show the extent to which training subjects to adjust their localization responses in one region of space affects how they localize sources in adjacent regions, and provide a measure of the spatial kernel that drives spatial auditory adaptation.

Prism adaptation to optical deviation alleviates pathologic pain

The human visual and somatosensory systems are interdependent. Using a visual subjective body-midline (SM) judgment task, we previously confirmed that pathologic pain and deafferentation can modify visuospatial perception, indicating that altered somatosensory experience can modify visual perception. Conversely, in the present study we investigated whether a change in visual experience can modify perception of pathologic pain. We used prism adaptation (PA) to modify subjects' visual experience. Five patients with complex regional pain syndrome (CRPS) adapted to wedge prisms, producing a 20-degree visual displacement toward the unaffected side. Further, we used several types of prisms in a longitudinal single-case study. Wearing prismatic goggles, the subjects performed a target-pointing task once a day for 2 weeks. We evaluated pain intensity and visual SM judgment to measure the adaptive aftereffects at three time points: before PA (pre-test), immediately after the first PA exposure (IA-test), and after a 14-day sequence of PA exposure (post-test). PA toward the unaffected side alleviated pathologic pain and other CRPS pathologic features, when measured at post-test. None of the IA-test results showed an analgesic effect. In the longitudinal study, sham PA and 5-degree PA did not produce any effects, and PA toward the affected side actually exacerbated the subjective pain. Our findings suggest that vision can influence pathologic pain, and preliminarily suggest that prism adaptation has a direction-specific and reproducible effect on not only pathologic pain but also other CRPS pathologic features. Thus, prism adaptation may be a viable cognitive treatment for CRPS.

Information maximization in face processing

This perspective paper explores principles of unsupervised learning and how they relate to face recognition. Dependency coding and information maximization appear to be central principles in neural coding early in the visual system. These principles may be relevant to how we think about higher visual processes such as face recognition as well. The paper first reviews examples of dependency learning in biological vision, along with principles of optimal information transfer and information maximization. Next, we examine algorithms for face recognition by computer from a perspective of information maximization. The eigenface approach can be considered as an unsupervised system that learns the first- and second-order dependencies among face image pixels. Eigenfaces maximize information transfer only in the case where the input distributions are Gaussian. Independent component analysis (ICA) learns high-order dependencies in addition to first- and second-order relations, and maximizes information transfer for a more general set of input distributions. Face representations based on ICA gave better recognition performance than eigenfaces, supporting the theory that information maximization is a good strategy for high level visual functions such as face recognition. Finally, we review perceptual studies suggesting that dependency learning is relevant to human face perception as well, and present an information maximization account of perceptual effects such as the atypicality bias, and face adaptation aftereffects.

Modelling adaptation aftereffects in associative memory

We present a simple autoassociative neural network model of cortical adaptation that replicates a high-level category aftereffect. We study in our model the effect of a priming stimulus on retrieval from a briefly presented partial cue. We also explore, in our general framework, which learning conditions permit correct pattern retrieval.

Adaptation aftereffects in the perception of gender from biological motion

Human visual perception is highly adaptive. While this has been known and studied for a long time in domains such as color vision, motion perception, or the processing of spatial frequency, a number of more recent studies have shown that adaptation and adaptation aftereffects also occur in high-level visual domains like shape perception and face recognition. Here, we present data that demonstrate a pronounced aftereffect in response to adaptation to the perceived gender of biological motion point-light walkers. A walker that is perceived to be ambiguous in gender under neutral adaptation appears to be male after adaptation with an exaggerated female walker and female after adaptation with an exaggerated male walker. We discuss this adaptation aftereffect as a tool to characterize and probe the mechanisms underlying biological motion perception.

Long lasting aftereffect of a single prism adaptation: directionally biased shift in proprioception and late onset shift of internal egocentric reference frame

We aimed to dissociate components in prism adaptation and its aftereffect by using prism adaptation training in healthy humans. Arm proprioceptive aftereffects are usually measured by indicating the subjective straight ahead direction with eyes closed (S). This measure however could be affected by other components besides proprioception, such as an efferent motor component and internal egocentric reference frame. Here we report a very long lasting proprioceptive shift, detected by two measuring methods, that is a component of the adaptation aftereffects to left wedge prism glasses. In order to minimize possible active motor components, arm passive proprioceptive midsagittal judgment was measured (P). The subject's arm was passively brought from the right or left lateral position, and stopped by subjects' verbal order. The results from these different measurements of midsagittal judgment were compared for 7 days after prism adaptation. Surprisingly, we found two distinctly separate aftereffects of proprioceptive shift depending on the directions of the passive arm movement. The shift of the midsagittal plane appeared only when tested from the left (Pl). This indicates that our strong prism adaptation procedure affected proprioception in a directionally biased way and not a spatially ubiquitous way. Further, the early aftereffect seen in active straight ahead pointing (S) was mostly similar to this biased shift in proprioception (Pl). However the long lasting aftereffect in straight ahead pointing was independently maintained up to day 7, when the passive proprioception had returned to pretest level. These results indicate that active straight ahead pointing (S) involves other components in addition to the passively measurable proprioceptive component. We suggest a late onset shift in the internal egocentric reference frame is involved in S. Possible neural mechanisms for these phenomena are discussed.

Long-lasting aftereffect of a single prism adaptation: shifts in vision and proprioception are independent

After a single adaptation session to prisms with gradually incremented shift magnitude, the prism adaptation aftereffect was measured by open loop mid-sagittal pointing (O) to a visual target without visual feedback. This aftereffect corresponded to the summation of the shift in proprioception, measured by straight ahead pointing without vision (S), and the visual straight ahead judgement (V), measured by verbal stopping of an LED moving from two opposite directions. However, the measurement of the aftereffects made over a period of 7 days revealed significantly different decay curves in V, O and S. Surprisingly the S shift was still present up to 7 days after the training, while V had returned to the original level by 2 h, which was the first measurement after subjects returned to a normal visual environment. O had returned to pre-test level after 1 day. After 3 days Wilkinson's (J Exp Psychol 89:250-257, 1971) additive hypothesis (O=S-V) no longer fit the data. Rather "O=Pl-V", where Pl (Pr) is the shift in proprioception measured by passive lateral arm movements from left (right), fitted better during the whole 7 days of aftereffect in our study. Therefore, the aftereffect of our strong prism adaptation revealed, firstly, that classical open loop pointing consisted of aftereffect shifts equal to the summation of the shifts in the two passively measurable aftereffect components, vision (V) and proprioception (Pl), rather than with active straight ahead pointing (S). Secondly, the decay of the shift in visual perception and in passively measurable proprioception is independent. The former decays fast, and the latter decays slowly with two separate waves. Thirdly, we suggest that the use of visual perception-dependent spatial codes for visual-manual transformation and the vision-independent internal egocentric reference frame are mutually exclusive. We proposed a model to explain these possible mechanisms.

Demonstration of cue recruitment: change in visual appearance by means of Pavlovian conditioning.

Until half a century ago, associative learning played a fundamental role in theories of perceptual appearance [Berkeley, G. (1709) An Essay Towards a New Theory of Vision (Dublin), 1st Ed.]. But starting in 1955 [Gibson, J. J. & Gibson, E. J. (1955) Psychol. Rev. 62, 32-41], most studies of perceptual learning have not been concerned with association or appearance but rather with improvements in discrimination ability. Here we describe a "cue recruitment" experiment, which is a straightforward adaptation of Pavlov's classical conditioning experiment, that we used to measure changes in visual appearance caused by exposure to novel pairings of signals in visual stimuli. Trainees viewed movies of a rotating wire-frame (Necker) cube. This stimulus is perceptually bistable. On training trials, depth cues (stereo and occlusion) were added to force the perceived direction of rotation. Critically, an additional signal was also added, contingent on rotation direction. Stimuli on test trials contained the new signal but not the depth cues. Over 45 min, two of the three new signals that we tested acquired the ability to bias perceived rotation direction on their own. Results were consistent across the eight trainees in each experiment, and the new cue's effectiveness was long lasting. Whereas most adaptation aftereffects on appearance are opposite in direction to the training stimuli, these effects were positive. An individual new signal can be recruited by the visual system as a cue for the construction of visual appearance. Cue recruitment experiments may prove useful for reexamining of the role of experience in perception.

Two waves of a long-lasting aftereffect of prism adaptation measured over 7 days

Prism adaptation is a useful paradigm to study the integration and reorganization of various sensory modalities involved in sensory-motor tasks. By prolonging the prismatic aftereffect and well-timed observation, we aimed to dissociate the components and mechanisms involved in human prism adaptation by their differential decay and development time courses. Here, we show that a single session of prism adaptation training, combining small increments of prism strength below the subjects' awareness threshold, during a pointing task with a free walk session with total prism exposure duration of 75 min, generated a surprisingly long-lasting aftereffect. The aftereffect was measured by the magnitude of the proprioceptive shift (assessed by straight-ahead pointing in the dark) for 7 days. An aftereffect was observed, which lasted for more than 6 days, by a single prism adaptation session. The aftereffect did not decay gradually. Unlike previous descriptions, the aftereffect showed two separate time-courses of decay and increase. After a significant initial decay within 6 h, the aftereffect increased again from 1 day up to 3 days. The novel decay and delayed development profile of this adaptation aftereffect suggests two separate underlying neural mechanisms with different time scales. Our experimental paradigms promise to reveal directly the temporal characteristics of early versus late long-term neural plasticity in complex human adaptive behavior.

Spatiotopic Transfer of Visual-Form Adaptation across Saccadic Eye Movements

Although conscious perception is smooth and continuous, the input to the visual system is a series of short, discrete fixations interleaved with rapid shifts of the eye. One possible explanation for visual stability is that internal maps of objects and their visual properties are remapped around the time of saccades, but numerous studies have demonstrated that visual patterns are not combined across saccades. Here, we report that visual-form aftereffects transfer across separate fixations when adaptor and test are presented in the same spatial position. The magnitude of the transsaccadic adaptation increased with stimulus complexity, suggesting a progressive construction of spatiotopic receptive fields along the visual-form pathway. These results demonstrate that basic shape information is combined across saccades, allowing for predictive and consistent information from the past to be incorporated into each new fixation.

The stickiness of face adaptation aftereffects

Face adaptation aftereffects have been assumed to disappear rapidly with time and/or interference, as do standard adaptation effects in low-level vision. Our results challenge this assumption. We considered two adapter duration procedures: a 160 s adapter period with separate pre- and post-adaptation phases; and a 5 s adapter period intermixed with post-adaptation trials. Each of these is similar to procedures used in previous studies. Our distortion types involved either radially compressing-expanding a face (where adaptation to a compressed face makes a normal face look expanded), or altering only the spacing between features so that the eyes were shifted up or down the head (where adapting to an eyes-down face makes a normal face appear to have its eyes shifted up). Results showed that, following a 160 s adapter period, significant adaptation survived a 15 min delay filled with visual stimulation; moreover, this occurred when the visual input involved only words and objects, and when many normal undistorted faces were included. For the 160 s adapter, a 24 hr delay removed the aftereffect. Following a 5 s adapter period, significant adaptation survived a 10 s delay including one face for 200 ms and either a normal face or an XXX stimulus for 5 s; indeed, inclusion of the filled delay only approximately halved the effect compared to immediate test. For the 5 s adapter, a 20 s delay with twice the number of intervening stimuli removed the aftereffect. Overall, we conclude that face aftereffects are much ‘stickier’ than traditional aftereffects. This has important implications for both theory and methodology. In terms of theory, we consider implications for neural coding models of the face aftereffects, and for the way in which the norm of face-space changes in response to recent input. In terms of methodology, our results argue it cannot be assumed that a short delay between testing adapter conditions is sufficient to remove carryover from the previous condition.

Adaptation to a novel multi-force environment

Humans display accurate limb behavior when they move in familiar environments composed of many simultaneously-acting forces. Little is known about how multi-force environments are represented and whether this process partitions between the underlying force components, reflects the net forces present, or is cued to the force-context. We tested between these three main alternatives by examining how reaching movements adapt to a novel multi-force field composed of a velocity-dependent force and a constant force. These hypotheses were dissociated first by making the constant force larger and oppositely-oriented to the velocity-dependent force; thereby, the net force was always opposite the velocity-dependent component. Second, we tested adaptation with all novel forces removed to eliminate any potential cues for the force-context. In two experiments that used forces perpendicular or parallel to the forward movement direction, we found adaptation aftereffects consistent with a mechanism that partitioned the velocity-dependent component from the net force field. Specifically, we found aftereffects opposite the rightward or resistive velocity-dependent component of the multi-force field, even though the net force imposed was leftward or assistive, respectively. An additional experiment suggested that the velocity-dependent component is partitioned relative to the background load in a limb-based coordinate frame.

Aftereffect of adaptation to Glass patterns

Our visual systems constantly adapt their representation of the environment to match the prevailing input. Adaptation phenomena provide striking examples of perceptual plasticity and offer valuable insight into the mechanisms of sensory coding. Here, we describe an aftereffect of adaptation to a spatially structured image whereby an unstructured test stimulus takes on illusory structure locally perpendicular to that of the adaptor. Objective measurement of the strength of the aftereffect for different patterns suggests a neural locus of adaptation prior to the extraction of complex form in the visual processing hierarchy, probably at the level of primary visual cortex. This view is supported by further experiments showing that the aftereffect exhibits partial interocular transfer but complete transfer across opposite contrast polarities. However, the aftereffect does show weak position invariance, suggesting that adaptation at higher levels of the visual system may also contribute to the effect.

Learning a new cue for motion in depth

To optimally exploit the statistical structure in signals produced by the visual environment, the visual system ought to learn when a signal that was previously uninformative becomes useful for inferring a property of the world. If the visual system can learn to use a newly reliable signal, one would expect to see effects of the new signal on both decisions at threshold (Ernst & Jäkel, VSS 2003) and on visual percepts. We designed a test of these propositions, using a task in which observers judge direction of motion-in-depth for a stereoscopically defined surface. The signals for motion-in-depth (vergence and looming) can be precisely controlled. The surface rotates about the cyclopean line of sight, at an angular velocity that is either proportional to speed in depth, or else uncorrelated with speed in depth, depending on the training group to which the observer is assigned; this rotation is the new cue for motion-in-depth. On a small number of probe trials in the Correlated condition, angular velocity is reversed. If rotation is recruited as a new cue by the visual system, it will influence both thresholds and motion-in-depth judgments. Data from correlated and uncorrelated training conditions will be reported. We make several points: (1) Adaptation phenomena (“normalizations”) that recalibrate perception relative to a previously learned Bayesian prior are different from cue recruitment, and cause negative, rather than positive, adaptation aftereffects. (2) We suppose that the visual system can learn that signals are uncorrelated. An ideal learner ought therefore to learn new associations between signals slowly, if at all, if the signals have been reliably uncorrelated in the past. (3) Learning may be facilitated by practice at threshold, where the new signal is actually of use to the visual system in making discriminations. (4) A complete theory would need to explain the extent to which learning is context dependent. EY013988