Direct-effects and after-effects of dynamic adaptation on intralimb and interlimb transfer

After-effects following sensorimotor adaptation are generally considered as evidence for the formation of an internal model, although evidence lacks on whether the absence of after-effects necessarily indicates that the adaptation did not result in the formation of an internal model. Here, we examined direct- and after-effects of dynamic adaptation with one arm at one workspace on subsequent performance with the other arm, as well as the same arm at another workspace. During training, subjects performed reaching movements under a novel dynamic condition with the right arm; during testing, they performed reaching movements with the left or right arm at a new workspace, under either the same dynamic condition (direct-effects) or a normal condition (after-effects). Results showed significant transfer within the same arm in terms of both direct- and after-effects, but significant transfer across the arms only in terms of direct-effects. These findings suggest that the formation of an internal model does not always result in after-effects. They also support the idea that the neural representation developed after sensorimotor adaptation comprise some aspects that are effector independent and other aspects that are effector dependent; and that direct- and after-effects following sensorimotor adaptation mainly reflect the effector-independent and the effector-dependent aspects, respectively.     

The nature and duration of adaptation following long-term odor exposure

Any individual living or working in an odorous environment can experience changes in odor perception, some of which are long lasting. Often, these individuals report a significant reduction in the perception of an odor following long-term exposure to that odor (adaptation). Yet, most experimental analyses of olfactory adaptation use brief odorant exposures which may not typify real-world experiences. Using a procedure combining long-term odor exposure in a naturalistic setting with psychophysical tests in the laboratory, we present evidence to show that reduced odor intensity following long-term exposure is accompanied by odorant-specific shifts in threshold. Subjects were exposed continuously to one of two odorants while in their home for a period of 2 weeks. Exposure produced an odorant-specific reduction in sensitivity and perceived intensity compared with preexposure baselines: Detection thresholds for the adapting odorant were elevated following exposure and perceived intensity ratings for weak concentrations were reduced. For most individuals, reduced sensitivity to the test odorant was still evident up to 2 weeks following the last exposure. The persistence of the change, as evidenced by the duration of recovery from adaptation, distinguishes this phenomenon from the adaptation seen following shorter exposures and highlights the need for the study of exposure durations that are more similar to real-world exposures.     

Modulation of gait during visual adaptation to dark

The authors investigated the modulation of gait during dark adaptation. Twenty-five women (mean age = 72 years, SD = 5 years) walked back and forth on an arbitrarily uneven walkway during normal lighting at speeds ranging from slow to fast. Participants then performed 20 trials at preferred speed after sudden reduction of lighting; the authors compared those trials with point estimates at equivalent speeds representing normal lighting. The authors estimated speed, cadence, mediolateral trunk acceleration, and mediolateral interstep trunk-acceleration variability for each trial. Participants compensated for sudden reduction of lighting by reducing their walking speed. Compared with performance at equivalent speeds during normal lighting, cadence, trunk acceleration, and interstep trunk-acceleration variability initially increased. All variables showed an asymptotic approximation toward normal values during 60-90 s of walking in subdued lighting. The authors suggest that the sudden transition from normal to marginal lighting, rather than marginal lighting itself, may challenge locomotor control.     

Loss of latent inhibition in conditioned taste aversion following exposure to a novel flavour before test

Killcross, Kiernan, Dwyer, andWestbrook (1998b) observed that latent inhibition(LI) of contextual fear was attenuated if animals received post-conditioning exposure to a novel context similar to the pre-exposure context. Six experiments used a conditioned taste aversion (CTA) procedure to examine this effect. Experiments 1A-1C demonstrated that LI of CTA was attenuated by a similar post-conditioning manipulation, establishing the generality of previous findings. Experiment 2A manipulated the taste elements to which animals were exposed after conditioning, revealing that exposure to a common element X, present at pre-exposure and conditioning, was not responsible for loss of LI. Experiment 2B manipulated test solution and showed that loss of LI depended on the presence of the full pre-exposed cue AX at test. These two results are contrary to predictions derived from the Dickinson-Burke (Dickinson & Burke, 1996) theory of retrospective revaluation or comparator theory (Miller & Matzel, 1988), and they support recent findings suggesting that retrospective effects may occur by several mechanisms. Experiment 3 showed that a novel element B had to be present during post-conditioning exposure for an attenuation of LI to be observed. Implications for the loss of LI following aretention interval between conditioning and test and retrieval-failure theories of LI are discussed.     

First-trial adaptation to prism exposure: artifact of visual capture

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than is expected from the optical displacement magnitude. The authors confirmed 1st-trial adaptation in the task of pointing toward optically displaced targets while visual feedback was delayed until movement completion. Measurement of head-shoulder posture while participants (N = 24) viewed the optically displaced field revealed that their shoulders felt turned in the direction opposite to the displacement (visual capture), accounting for all but about 4% to 10% of 1st-trial adaptation. First-trial adaptation was unrelated to realignment aftereffects. First-trial adaptation is largely an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt body rotation, thereby reducing the effective optical 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.     

A comparison of repeated exposure to fearful and disgusting stimuli among spider phobics

This study examined the role of fear and disgust in repeated exposure among spider phobics. Thirty spider phobics were randomly assigned to one of two experimental groups. Both groups completed measures of fear and disgust and performed two initial standardized Behavioral Avoidance Tests (BATs; one with a fear stimulus – live tarantula, and one with a disgust stimulus – dead rat). One group was then repeatedly exposed to the tarantula and the other to the dead rat. Results of the study indicated that exposure to either the disgust stimulus or the live tarantula was associated with significant decreases in fear, avoidance, and disgust. However, it was found that repeated exposure to the fear stimulus produced a greater decrease in avoidance behavior. Results suggest that both types of exposure can be effective in alleviating associated symptoms and provide additional evidence that disgust sensitivity plays a role in the treatment of spider phobia. Copyright © 2010 John Wiley & Sons, Ltd.     

Superiority of variable to repeated practice in transfer on anagram solution

Previous research in motor learning shows that practicing variations of a task (variable practice) leads to better transfer than does repeatedly practicing the exact same task (repeated practice). In contrast, research on priming using verbal materials shows that performance on a test improves to the extent that the material at learning and test overlap. We tested whether variability in practice conditions can lead to improved performance with the verbal priming task of anagram solution. Participants practiced solving anagrams, either repeatedly solving the same anagram that was later tested, repeatedly solving a different anagram from the one that was later tested, or solving different variations of the anagram that was later tested. We found that this last condition-variable practice on different versions of an anagram-led to improved test performance in relation to repeated practice, even when the test anagram was the one that had been repeatedly practiced. This finding aligns results from the motor learning literature with a higher level cognitive task: anagram solution. Shea and Kohl's (1991) hypothesis, arguing that varied practice may lead to greater elaborative processing than does repeated practice, provides one account of the results.     

Effects of homogeneous and variable exposure on magnitude of adaptation to optical tilt

Repeated exposure to hallway exploration, alternated with periods of either watching the active hand or exploring a different set of hallways, maintains increasing visual adaptation beyond the point in time at which previous studies using homogeneous exposure have found such visual shift (VS) to be asymptotic. Experiment 1 established that this alternation-repetition effect does not depend on an actual change in task (hall to hand) but also occurs when the task context alone is changed (hall to hall). Experiment 2 compared variable (hall-to-hall) exposure with homogeneous (hall) exposure, showing that variable exposure removes the usual limit on adaptation. In both experiments, proprioceptive shift (PS) and total negative aftereffect (NA) both tended to be less than VS, producing substantial overadditivity (i.e., VS + PS greater than NA). General requirements for an attentional explanation of the alternation-repetition effect are outlined, and possible explanations of overadditivity consistent with the linear model are discussed.     

Alternating prism exposure causes dual adaptation and generalization to a novel displacement

In two experiments, we examined the hypothesis that repeatedly adapting and readapting to two mutually conflicting sensory environments fosters the development of a separate adaptation to each situation (dual adaptation) as well as an increased ability to adapt to a novel displacement (adaptive generalization). In the preliminary study, subjects alternated between adapting their visuomotor coordination to 30-diopter prismatic displacement and readapting to normal vision. Dual adaptation was observed by the end of 10 alternation cycles. However, an unconfounded test of adaptive generalization was prevented by an unexpected prism-adaptive shift in preexposure baselines for the dual-adapted subjects. In the primary experiment, the subjects adapted and readapted to opposite 15-diopter displacements for a total of 12 cycles. Both dual adaptation and adaptive generalization to a 30-diopter displacementwere obtained. These findings may be understood in terms of serial reversal learning and “learning to learn.”     

Immediate and delayed transfer of training effects in statistical reasoning

Ss were trained on the law of large numbers in a given domain through the use of example problems. They were then tested either on that domain or on another domain either immediately or after a 2-week delay. Strong domain independence was found when testing was immediate. This transfer of training was not due simply to Ss' ability to draw direct analogies between problems in the trained domain and in the untrained domain. After the 2-week delay, it was found that (a) there was no decline in performance in the trained domain and (b) although there was a significant decline in performance in the untrained domain, performance was still better than for control Ss. Memory measures suggest that the retention of training effects is due to memory for the rule system rather than to memory for the specific details of the example problems, contrary to what would be expected if Ss were using direct analogies to solve the test problems.     

Fear and disgust processing during repeated exposure to threat-relevant stimuli in spider phobia

Although disgust plays a significant role in the etiology of spider phobia, there remains a paucity of research examining the role of disgust in the treatment of spider phobia. Spider fearful participants (N = 46) were randomly assigned to a disgust (view vomit images) or neutral activation (view inanimate objects) condition. They were then repeatedly exposed to a videotaped tarantula, during which time their fear, disgust, and physiological levels were assessed repeatedly. Growth curve analyses indicated that repeated exposure led to significant declines in fear and disgust with no statistically significant differences between the two conditions. However, there was marginal evidence for decreased physiological arousal during repeated exposure among spider fearful participants in the disgust activation condition compared to those in the neutral condition. Reduction in disgust during exposure in the disgust activation condition remained significant after controlling for change in fear, whereas change in fear was no longer significant after controlling for change in disgust. However, the opposite pattern of relations between change in fear and disgust was observed in the neutral activation condition. Higher fear and disgust activation during exposure was also associated with higher fear and disgust responding on a subsequent behavioral task and higher spider fear and disgust at 3-month follow-up. Baseline trait disgust propensity also predicted fear and disgust parameters during repeated exposure. The implications of these findings for the role of disgust in the treatment of spider phobia are discussed.