Constraints on perceptual learning: objects and dimensions

A condition that produces sensory recalibration and abolishes multisensory integration

We examined the influence of extended exposure to a visuomotor rotation, which induces both motor adaptation and sensory recalibration, on (partial) multisensory integration in a cursor-control task. Participants adapted to a 30° (adaptation condition) or 0° (control condition) visuomotor rotation by making center-out movements to remembered targets. In subsequent test trials of sensory integration, they made center-out movements with variable visuomotor rotations and judged the position of hand or cursor at the end of these movements. Test trials were randomly embedded among twice the number of maintenance trials with 30° or 0° rotation. The biases of perceived hand (or cursor) position toward the cursor (or hand) position were measured. We found motor adaptation together with proprioceptive and visual recalibrations in the adaptation condition. Unexpectedly, multisensory integration was absent in both the adaptation and control condition. The absence stemmed from the extensive experience of constant visuomotor rotations of 30° or 0°, which probably produced highly precise predictions of the visual consequences of hand movements. The frequently confirmed predictions then dominated the estimate of the visual movement consequences, leaving no influence of the actual visuomotor rotations in the minority of test trials. Conversely, multisensory integration was present for sensed hand positions when these were indirectly assessed from movement characteristics, indicating that the relative weighting of discrepant estimates of hand position was different for motor control. The existence of a condition that abolishes multisensory integration while keeping sensory recalibration suggests that mechanisms that reduce sensory discrepancies (partly) differ between integration and recalibration.

Inter-task transfer of prism adaptation depends on exposed task mastery

The sensorimotor system sets up plastic alterations to face new demands. Terms such as adaptation and learning are broadly used to describe a variety of processes underlying this aptitude. The mechanisms whereby transformations acquired to face a perturbation generalize to other situations or stay context-dependent remain weakly understood. Here, we compared the performance of hand pointing vs throwing to visual targets while facing an optical shift of the visual field (prismatic deviation). We found that the transfer of compensations was conditioned by the task performed during exposure to the perturbation: compensations transferred from pointing to throwing but not at all from throwing to pointing. Additionally, expertise on the task performed during exposure had a marked influence on the amount of transfer to the non-exposed task: throwing experts (dart players) remarkably transferred compensations to the pointing task. Our results reveal that different processes underlying these distinct transfer properties may be at work to face a given perturbation. Their solicitation depends on mastery for the exposed task, which is responsible for different patterns of inter-task transfer. An important implication is that transfer properties, and not only after-effects, should be included as a criterion for adaptation. At the theoretical level, we suggest that tasks may need to be mastered before they can be subjected to adaptation, which has new implications for the distinction between learning and adaptation.

Influence of Visual Prism Adaptation on Auditory Space Representation

Prisms shifting the visual input sideways produce a mismatch between the visual versus felt position of one’s hand. Prism adaptation eliminates this mismatch, realigning hand proprioception with visual input. Whether this realignment concerns exclusively the visuo-(hand)motor system or it generalizes to acoustic inputs is controversial. We here show that there is indeed a slight influence of visual adaptation on the perceived direction of acoustic sources. However, this shift in perceived auditory direction can be fully explained by a subconscious head rotation during prism exposure and by changes in arm proprioception. Hence, prism adaptation does only indirectly generalize to auditory space perception.

Prior Visual Experience Modulates Learning of Sound Localization Among Blind Individuals

Cross-modal learning requires the use of information from different sensory modalities. This study investigated how the prior visual experience of late blind individuals could modulate neural processes associated with learning of sound localization. Learning was realized by standardized training on sound localization processing, and experience was investigated by comparing brain activations elicited from a sound localization task in individuals with (late blind, LB) and without (early blind, EB) prior visual experience. After the training, EB showed decreased activation in the precuneus, which was functionally connected to a limbic-multisensory network. In contrast, LB showed the increased activation of the precuneus. A subgroup of LB participants who demonstrated higher visuospatial working memory capabilities (LB-HVM) exhibited an enhanced precuneus-lingual gyrus network. This differential connectivity suggests that visuospatial working memory due to the prior visual experience gained via LB-HVM enhanced learning of sound localization. Active visuospatial navigation processes could have occurred in LB-HVM compared to the retrieval of previously bound information from long-term memory for EB. The precuneus appears to play a crucial role in learning of sound localization, disregarding prior visual experience. Prior visual experience, however, could enhance cross-modal learning by extending binding to the integration of unprocessed information, mediated by the cognitive functions that these experiences develop.

Visual Recalibration of Auditory Speech Identification

The kinds of aftereffects, indicative of cross-modal recalibration, that are observed after exposure to spatially incongruent inputs from different sensory modalities have not been demonstrated so far for identity incongruence. We show that exposure to incongruent audiovisual speech (producing the well-known McGurk effect) can recalibrate auditory speech identification. In Experiment 1, exposure to an ambiguous sound intermediate between /aba/ and /ada/ dubbed onto a video of a face articulating either /aba/ or /ada/ increased the proportion of /aba/ or /ada/ responses, respectively, during subsequent sound identification trials. Experiment 2 demonstrated the same recalibration effect or the opposite one, fewer /aba/ or /ada/ responses, revealing selective speech adaptation, depending on whether the ambiguous sound or a congruent nonambiguous one was used during exposure. In separate forced-choice identification trials, bimodal stimulus pairs producing these contrasting effects were identically categorized, which makes a role of postperceptual factors in the generation of the effects unlikely.

Spatial action-effect binding

The temporal interval between an action and its ensuing effect is perceptually compressed. Specifically, the perceived onset of actions is shifted towards their effects in time and, vice versa, the perceived onset of effects is shifted towards their causing actions. In four experiments, we report evidence showing that action-effect binding also occurs in the spatial domain. Participants controlled the location of a visual stimulus by performing stylus movements before they judged either the position of the stylus or the position of the visual stimulus. The results yielded spatial binding between the perceived stylus position and the perceived stimulus position when the stimulus was under full control of the hand movement compared to control conditions without direct control.

Perception of the Mccollough Effect Correlates with Activity in Extrastriate Cortex: A Functional Magnetic Resonance Imaging Study

The McCollough effect is a striking color aftereffect that is linked to the orientation of the patterns used to induce it. To produce the McCollough effect, two differently oriented grating patterns, such as a red-and-black vertical grating and a green-and-black horizontal grating, are viewed alternately for a few minutes. After such colored gratings are viewed, the white sections of a vertical black-and-white test grating appear to be tinged with green, and the white sections of a horizontal grating appear to be tinged with pink. We present evidence from a functional magnetic resonance imaging study that the perception of the McCollough effect correlates with increased activation in the lingual and fusiform gyri—extrastriate visual areas that have been implicated in color perception in humans.

The widespread influence of the Rescorla-Wagner model

The theory of Pavlovian conditioning presented by Robert Rescorla and Allan Wagner in 1972 (the Rescorla-Wagner model) has been enormously important in animal learning research. It also has been applied in a variety of areas other than animal learning. We summarize the contribution of the Rescorla-Wagner model to research in verbal learning, social psychology, human category learning, human judgments of correlational relationships, transitive inference, color aftereffects, and physiological regulation. We conclude that there have been few models in experimental psychology as influential as the Rescorla-Wagner model.

Towards mastery of complex visuo-motor transformations

In this paper we review and integrate a set of findings on learning the transformation of a sliding first-order lever, a type of tool with a prominent role in minimal access surgery. Its kinematic transformation is characterized by the so-called fulcrum effect, the inversion of the movement direction of the tip of the lever relative to that of the hand for rotations. A second characteristic is gain anisotropy, which results in curved paths of the tip of the lever for straight paths of the hand and vice versa. An internal model of the kinematic transformation is acquired during practice, the accuracy of which can be assessed in visual open-loop test trials. The accuracy of the acquired internal model is enhanced when visual closed-loop control during practice is impeded, and the accuracy of the internal model is reduced when closed-loop control during practice is facilitated. The internal model consists of a rapidly acquired line-symmetric approximation to the transformation of the sliding lever and a slowly acquired fine tuning. The fine tuning is local, that is, it is specific for the region of the workspace encountered during practice. The internal model is transferred to other regions of the workspace, but not adjusted to the fine tuning appropriate for these regions. Whereas the symmetry approximation is most likely explicit, the fine tuning seems to be represented implicitly. Findings on the straightness of the paths of the tip of the lever and the hand suggest that the internal model of the transformation is confined to initial and final positions of aimed movements, whereas their path is not strictly controlled, but affected by the dynamic transformation of the tool. Only when visual closed-loop control is possible, the path of the effective part of the tool is straightened. These characteristics of the internal model of the sliding first-order lever and its acquisition may be partly specific to sufficiently complex extrinsic transformations that arise from mechanical or electronic extensions of the body.

Adaptation to novel visuo-motor transformations: further evidence of functional haptic neglect

Studies with perturbed and augmented haptic information during adaptation to novel visuo-motor transformations suggest that haptic information might be neglected. However, the notion of functional haptic neglect during adaptation is counterintuitive for different reasons. Therefore, we sought conditions where haptic guidance during adaptation results in benefits. First, we mixed guided and unguided trials during practice with a visuo-motor rotation. In two experiments, we found no indication of an advantage of the guidance groups over the no-guidance control groups. In the third experiment, the visuo-motor transformation was a pure time delay because motor timing has been hypothesized to profit from haptic guidance. Again, there was no evidence of benefits for the guidance group. Thus, the findings of this series of experiments provide further evidence of the claim that haptic information is neglected during adaptation to a visuo-motor transformation.

Mystery of the anti-McCollough effect

The McCollough Effect (ME) is a complex perceptual aftereffect that remains of interest half a century after its discovery. It is argued that a recently reported variant, dubbed the anti-McCollough effect, is not the reverse of the ME, with aftereffect colors in the same direction as the inducing stimuli. A red-horizontal stimulus leads to a reddish aftereffect not because of red-horizontal parings, but despite them. The anti-ME is a weak standard-direction ME produced by complementary afterimage colors (afterimage green with horizontal), rather than by environmental colors, first shown decades ago. It is not a new type of contingent aftereffect. The red-horizontal pair does not interfere with the afterimage green-horizontal pair it produces because a single color-orientation pairing provides more ambiguous input than does the standard two orientation-color pairings (red-horizontal, green-vertical) of the ME. It is also argued that not even one orientation-contingent color aftereffect is convincingly shown in the "anti"-ME, let alone, as has previously been suggested, two simultaneous orientation-contingent color aftereffects in opposite directions at different levels of the visual system, in which the higher-level effect suppresses the downstream effect from reaching consciousness. The "anti"-ME can be explained by existing theories of contingent aftereffects, including perceptual-learning theory.

Using structural equation modeling to examine McCollough Effects (orientation-contingent color aftereffects): influence of dissociative experiences and age on illusory aftereffects

Conventional accounts of the McCollough Effect (ME) have focused on strictly bottom-up processing accounts of the phenomenon, most commonly involving the fatiguing of orientation-selective neurons; although association-learning mechanisms have also gained acceptance. These lower order accounts do not take into account higher order variables related to key personality traits and/or associated cognitive control processes. This article reports the use of confirmatory factor analysis and follow-up structural equation style regressions that model MEs and also the part played by the personality trait of dissociation. After considering the relative impact of age and dissociative processes, the article concludes that trait dissociation is positively associated with reports of MEs.

Implicit and explicit adjustments to extrinsic visuo-motor transformations and their age-related changes

Humans have unique abilities in using tools. The skilled and goal-directed use of a tool implies that processes of motor control can be adjusted to the transformation of the movement of a part of the body into the movement of the effective part of the tool. A common example is the transformation of a hand movement in the motion of a cursor on a computer monitor. In part the adjustments to such transformations are implicit, that is, without conscious awareness of the novel transformation and the appropriate change of one's own movements. However, the adjustments can also be explicit and intentional. We review a series of experiments which show that implicit and explicit adjustments to a novel visuo-motor gain are additive. This finding suggests that the processes which generate different types of adjustment are functionally independent. In a second series of experiments it turned out that at older adult age explicit adjustments to novel visuo-motor transformations are impaired, whereas implicit adjustments remain unaffected across working age.

Adapting internal statistical models for interpreting visual cues to depth

The informativeness of sensory cues depends critically on statistical regularities in the environment. However, statistical regularities vary between different object categories and environments. We asked whether and how the brain changes the prior assumptions about scene statistics used to interpret visual depth cues when stimulus statistics change. Subjects judged the slants of stereoscopically presented figures by adjusting a virtual probe perpendicular to the surface. In addition to stereoscopic disparities, the aspect ratio of the stimulus in the image provided a "figural compression" cue to slant, whose reliability depends on the distribution of aspect ratios in the world. As we manipulated this distribution from regular to random and back again, subjects' reliance on the compression cue relative to stereoscopic cues changed accordingly. When we randomly interleaved stimuli from shape categories (ellipses and diamonds) with different statistics, subjects gave less weight to the compression cue for figures from the category with more random aspect ratios. Our results demonstrate that relative cue weights vary rapidly as a function of recently experienced stimulus statistics and that the brain can use different statistical models for different object categories. We show that subjects' behavior is consistent with that of a broad class of Bayesian learning models.

Perceptual learning of co-articulation in speech

Four experiments investigated the novel issue of learning to accommodate the coarticulated nature of speech. Experiment 1 established a co-articulatory mismatch effect for a set of vowel-consonant (VC) syllables (reaction times were faster for co-articulation matching than for mismatching stimuli). A rhyme judgment training task on words (Experiment 2) or VC stimuli (Experiment 3) with mismatching information was followed by a phoneme monitoring task on a set of VC stimuli; training and test stimuli contained physically identical (same condition) or new (different condition) mismatching coarticulatory information (along with a set containing matching coarticulatory information). A third group received no training. A coarticulatory mismatch effect was found without training but not when the same mismatching tokens were used at training and test. Both word (Experiment 2) and syllable (Experiment 3) training stimuli eliminated the mismatch effect; overall reaction times were somewhat slower when the training stimuli were words. Perceptual learning generalized to new tokens only when the acoustic manifestation of the critical co-articulatory information in the training stimuli was sufficiently large (Experiments 3 and 4). The results are discussed in terms of speech processing and perceptual learning in speech perception.

Can a space-perception conflict be solved with three sense modalities?

A cross-modal conflict over location was resolved in an unexpected way. When vision and proprioception provide conflicting information, which modality should dominate is ambiguous. A visual-proprioceptive conflict was created with a prism and, to logically disambiguate the problem, auditory information was added that either agreed with vision (group 1), agreed with proprioception (group 2), or was absent (group 3). While a scarcity of research addresses the interaction of three modalities, I predicted error should be attributed to the modality in the minority. Instead, the opposite was found: adaptation consisted of a large change in arm proprioception and a small change affecting vision in group 2, and the reverse in group 1. Group 1 was not different than group 3. Findings suggested adaptation to separate two-way conflicts, possibly influenced by direction of attention, rather than a direct solution to a three-way modality problem.

Constraints on visuo-motor adaptation depend on the type of visual feedback during practice

Adaptation to a novel visuo-motor gain has been found to generalize across target directions, whereas simultaneous adaptation to different direction-related visuo-motor gains turned out to be impossible. We ask whether this is a rigid constraint on human adaptability or a soft constraint that can be overcome by optimized conditions of practice. In particular, we compared practice with continuous visual feedback, as used in previous studies, to practice with terminal visual feedback. With terminal visual feedback only the final positions of the movements are shown. Both kinds of visual feedback in principle can serve the acquisition of an internal model of direction-related visuo-motor gains, but with continuous feedback on-line visual closed-loop control permits accurate movements without access to an internal model. Whereas we found no indication of visuo-motor adaptation after continuous-feedback practice, there was adaptation after terminal-feedback practice. This was revealed both by (direction-related) adaptive shifts of movement amplitudes in an open-loop test with cued visuo-motor transformation and by (direction-related) aftereffects in an open-loop test with absence of the visuo-motor transformation being cued. None of the two groups gave evidence of explicit knowledge of the direction-related visuo-motor gains. These findings show that constraints on human adaptability can depend on the kind of experience with visuo-motor transformations, in particular on the kind of feedback during practice.

Learning to smell the roses: experience-dependent neural plasticity in human piriform and orbitofrontal cortices

It is widely presumed that odor quality is a direct outcome of odorant structure, but human studies indicate that molecular knowledge of an odorant is not always sufficient to predict odor quality. Indeed, the same olfactory input may generate different odor percepts depending on prior learning and experience. Combining functional magnetic resonance imaging with an olfactory paradigm of perceptual learning, we examined how sensory experience modifies odor perception and odor quality coding in the human brain. Prolonged exposure to a target odorant enhanced perceptual differentiation for odorants related in odor quality or functional group, an effect that was paralleled by learning-induced response increases in piriform cortex and orbitofrontal cortex (OFC). Critically, the magnitude of OFC activation predicted subsequent improvement in behavioral differentiation. Our findings suggest that neural representations of odor quality can be rapidly updated through mere perceptual experience, a mechanism that may underlie the development of odor perception.

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.

Color constancy and the functional significance of McCollough effects

A central problem in visual perception concerns how humans perceive stable and uniform object colors despite variable lighting conditions (i.e. color constancy). One solution is to 'discount' variations in lighting across object surfaces by encoding color contrasts, and utilize this information to 'fill in' properties of the entire object surface. Implicit in this solution is the caveat that the color contrasts defining object boundaries must be distinguished from the spurious color fringes that occur naturally along luminance-defined edges in the retinal image (i.e. optical chromatic aberration). In the present paper, we propose that the neural machinery underlying color constancy is complemented by an 'error-correction' procedure which compensates for chromatic aberration, and suggest that error-correction may be linked functionally to the experimentally induced illusory colored aftereffects known as McCollough effects (MEs). To test these proposals, we develop a neural network model which incorporates many of the receptive-field (RF) profiles of neurons in primate color vision. The model is composed of two parallel processing streams which encode complementary sets of stimulus features: one stream encodes color contrasts to facilitate filling-in and color constancy; the other stream selectively encodes (spurious) color fringes at luminance boundaries, and learns to inhibit the filling-in of these colors within the first stream. Computer simulations of the model illustrate how complementary color-spatial interactions between error-correction and filling-in operations (a) facilitate color constancy, (b) reveal functional links between color constancy and the ME, and (c) reconcile previously reported anomalies in the local (edge) and global (spreading) properties of the ME. We discuss the broader implications of these findings by considering the complementary functional roles performed by RFs mediating color-spatial interactions in the primate visual system.

Analysis of a Constraint on Perception, Cognition, and Development: One Object, One Place, One Time

It has become increasingly common for theories to rely on a constraint that 1 object cannot be in more than 1 place at the same time. Analysis suggests that a 1 object-1 place-1 time constraint as literally stated is false, that a modified constraint is biased toward the visual modality, that it may not be a correct description of the physical world, is not true of how objects must appear on sensory surfaces, and does not mean that 2 simultaneous spatially separated samples must be interpreted as 2 different objects, even for vision. However, once such object numerosity or identity is determined in some other way, then a modified constraint can be used to trigger learning, such as prism adaptation. A far-removed implication is that "Where is an object?" may be a misleading question.

Thalamocortical dynamics of the McCollough effect: boundary-surface alignment through perceptual learning

This article further develops the FACADE neural model of 3-D vision and figure-ground perception to quantitatively explain properties of the McCollough effect (ME). The model proposes that many ME data result from visual system mechanisms whose primary function is to adaptively align, through learning, boundary and surface representations that are positionally shifted due to the process of binocular fusion. For example, binocular boundary representations are shifted by binocular fusion relative to monocular surface representations, yet the boundaries must become positionally aligned with the surfaces to control binocular surface capture and filling-in. The model also includes perceptual reset mechanisms that use habituative transmitters in opponent processing circuits. Thus the model shows how ME data may arise from a combination of mechanisms that have a clear functional role in biological vision. Simulation results with a single set of parameters quantitatively fit data from 13 experiments that probe the nature of achromatic/chromatic and monocular/binocular interactions during induction of the ME. The model proposes how perceptual learning, opponent processing, and habituation at both monocular and binocular surface representations are involved, including early thalamocortical sites. In particular, it explains the anomalous ME utilizing these multiple processing sites. Alternative models of the ME are also summarized and compared with the present model.

Do McCollough effects provide evidence for global pattern processing?

Contingent color aftereffects (CAEs, or McCollough effects) were induced using two pairs of orthogonally related patterns (horizontal/vertical and concentric/radial) to determine whether the CAEs of the four patterns are independent. Tests using composite test patterns (like those employed by Emerson, Humphrey, & Dodwell, 1985) suggested independent aftereffects. However, tests using unitary patterns indicated additive or competing effects of the four patterns in regions where line orientations were similar, and tests isolating such regions showed clear interactions between the pattern aftereffects. The results fail to support the claim that global (rather than local) features of the patterns control these CAEs.

Adapting to remapped auditory localization cues: a decision-theory model

This paper describes a model of adaptation to remapped auditory localization cues that is based on previous decision-theory models of psychophysical performance. The present model extends earlier work by explicitly assuming that past experience affects subject perception and by quantifying how training causes subjects' responses to evolve over time. The model makes quantitative predictions of total sensitivity, bias, and resolution for subjects involved in experiments investigating spatial auditory adaptation. One assumption of the model is that subjects cannot adapt to nonlinear rearrangements of localization cues, which is consistent with previous experimental reports in both audition (Shinn-Cunningham, Durlach, & Held, 1998b) and vision (Bedford, 1993). The model assumes that, in spatial adaptation experiments, subjects learn to interpret a continuous internal decision variable differently than normal; they do not learn to associate discrete stimulus-response pairs. This view is consistent with previous analyses of results from experiments investigating adaptation to visual rearrangement, as well as with the McCullough effect in vision (Bedford, 1993, 1995).

Keeping perception accurate

Perception should change if an error in perception is detected. Yet how can information that comes through the senses ever indicate that those very senses aren't accurate? Knowledge of objects that arises independently of sensory experience can be used to check the sensory information for errors. For instance, an a priori constraint that one object cannot be in two places at the same time would lead to error detection if the sensory systems suggest that one object is in two places. Variants on the classic prism-adaptation phenomenon have revealed new rules about changes in space perception. These variants involve specifying new unusual mappings between visual space and motor (proprioceptive) space, and testing for generalization to novel untrained locations. The research has suggested that there is a preference for changes in space perception that shift space rigidly everywhere, that shrink or expand space uniformly, and that preserve the one-to-one relationship between modalities. Finally, this review discusses the issue that perception must change to remain accurate in the face of childhood growth and adult drift.

Perceptual learning

Perceptual learning involves relatively long-lasting changes to an organism's perceptual system that improve its ability to respond to its environment. Four mechanisms of perceptual learning are discussed: attention weighting, imprinting, differentiation, and unitization. By attention weighting, perception becomes adapted to tasks and environments by increasing the attention paid to important dimensions and features. By imprinting, receptors are developed that are specialized for stimuli or parts of stimuli. By differentiation, stimuli that were once indistinguishable become psychologically separated. By unitization, tasks that originally required detection of several parts are accomplished by detecting a single constructed unit representing a complex configuration. Research from cognitive psychology, psychophysics, neuroscience, expert/novice differences, development, computer science, and cross-cultural differences is described that relates to these mechanisms. The locus, limits, and applications of perceptual learning are also discussed.

Deficit in learning of a motor skill requiring strategy, but not of perceptuomotor recalibration, with aging

We investigated the effect of aging on different aspects of motor skill learning using two computer-presented perceptuomotor tasks. The relationship between visual and proprioceptive feedback was transformed in the first task, which was open to the formation and use of strategies. This task was designed to lead to perceptuomotor adaptation that was then measured by performance on a very similar second task that was not open to the use of strategy task. Older participants showed impaired learning of the strategic task but not of the nonstrategic task. This is in line with the suggestion that the effect of aging on learning and memory may be to reduce working memory resources.

Isoluminance and contingent color aftereffects

In the typical induction of the orientation-contingent color aftereffect (CCAE), the stimuli are composed of elements that differ in both color and luminance. Three experiments are reported that show that chromatic contrast between stimulus elements is insufficient for the induction of the orientation-CCAE and that luminance contrast is necessary. These experiments expand on previous research concerned with the role of luminance contrast in the induction of orientation-CCAEs by eliminating alternative explanations.

Contingent color aftereffects: reassessing old conclusions

Although there is considerable evidence supporting an associative interpretation of contingent color aftereffects, there are data that appear inconsistent with this interpretation. New findings from seven experiments are presented indicating that, contrary to earlier claims, contingent color aftereffects are observed after induction with (1) single orthogonal black bars on colored backgrounds, (2) geometric forms, and (3) two orthogonal grids of the same color. The results of these experiments are relevant to an associative interpretation of contingent color aftereffects, as well as to assessing alternative interpretations of the phenomenon.

Visual aftereffect of texture density contigent on color of frame

An aftereffect of perceived texture density contingent on the color of a surrounding region is reported. In a series of experiments, participants were adapted, with fixation, to stimuli in which the relative density of two achromatic texture regions was perfectly correlated with the color presented in a surrounding region. Following adaptation, the perceived relative density of the two regions was contingent on the color of the surrounding region or of the texture elements themselves. For example, if high density on the left was correlated with a blue surround during adaptation (and high density on the right with a yellow surround), then in order for the left and right textures to appear equal in the assessment phase, denser texture was required on the left in the presence of a blue surround (and denser texture on the right in the context of a yellow surround). Contingent aftereffects were found (1) with black-and-white scatter-dot textures, (2) with luminance-balanced textures, and (3) when the texture elements, rather than the surrounds, were colored during assessment. Effect size was decreased when the elements themselves were colored, but also when spatial subportions of the surround were used for the presentation of color. The effect may be mediated by retinal color spreading (Pöppel, 1986) and appears consistent with a local associative account of contingent aftereffects, such as Barlow's (1990) model of modifiable inhibition.