Conditioned adaptation to prismatic displacement with a tone as the conditional stimulus

Adaptation to prismatic displacement was conditioned to a tone in 72 min of training by employing Taylor’s alternation training technique. The alternation consisted of two training conditions. In one, S was exposed to the prism and tone; in the other, S was exposed to neither. After training, the pointing to a visual target test measured more aftereffects of adaptation when the tone was present than when it was absent. Conditioning was obtained in two testing situations: (1) with the training goggles still worn by S, and (2) with the goggles removed.     

Discriminative conditioning of prism adaptation

Two experiments were used to demonstrate that adaptation to ll-deg prism displacement can be conditioned to the stimuli associated with the goggles in which the prisms are housed. In Experiment 1 it was found that repeated alternation between a series of target-pointing responses while wearing prism goggles and a series of responses without prism goggles led to larger adaptive shift when S was tested with nondisplacing goggles than when tested without goggles. The results of Experiment 2 indicated that the adaptation revealed in the first experiment was primarily proprioceptive, rather than visual. Surprisingly, most Ss reported greater difficulty during the exposure period in overcoming the negative aftereffect than they did the prism-induced error.     

The whole-hand point: the structure and function of pointing from a comparative perspective

Pointing by monkeys, apes, and human infants is reviewed and compared. Pointing with the index finger is a species-typical human gesture, although human infants exhibit more whole-hand pointing than is commonly appreciated. Captive monkeys and feral apes have been reported to only rarely "spontaneously" point, although apes in captivity frequently acquire pointing, both with the index finger and with the whole hand, without explicit training. Captive apes exhibit relatively more gaze alternation while pointing than do human infants about 1 year old. Human infants are relatively more vocal while pointing than are captive apes, consistent with paralinguistic use of pointing.     

Adaptation to prisms: Do proprioceptive changes mediate adapted behaviour with ballistic arm movements?

In Experiment I subjects pointed repeatedly at a target viewed through laterally displacing prisms and received terminal visual feedback. In one task the pointing movements were slow (proprioceptively controlled), and in the other they were fast (pre-programmed). In both tasks adaptation proceeded at the same rate and to the same level of performance. Following fast pointing with prisms a large amount of arm-body adaptation was found with slow and fast test movements, while following slow pointing with prisms a large amount of arm-body adaptation was found with slow test movements, but only a small amount with fast test movements. The result suggests that adapted behaviour with preprogrammed movements is not mediated by a proprioceptive change. In Experiment II pointing movements were passive. No arm-body adaptation was found with fast test movements, and, contrary to expectation, only a small amount with slow test movements.     

Two kinds of adaptation in the constancy of visual direction and their different effects on the perception of shape and visual direction

Adaptation in the constancy of visual direction can be obtained under two radically different conditions, called eye-movement adaptation and field adaptation. Adaptation resulting from these conditions and from a “normal” condition was measured with a newly developed estimation test. Eye-movement adaptation was found to cause an alteration of compensatory eye movements. It apparently consists of a changed evaluation of eye movements, as demonstrated by two different pointing tests. A form test where the shape of a large oblong is set to look square also confirmed this interpretation. After field adaptation, a pointing test did not register a change, but an adaptation effect could be measured with a forward direction test. This test and a square test where no eye movements were permitted proved to be specific to field adaptation; they measured no effect after eye-movementadaptation. The normal adaptation condition Was apparently equivalent to the eye-movement adaptation condition. Its effect could be measured only with a pointing test. When we changed the normal adaptation condition so that frequent saccades were made during head turning, strong effects were measured with the two tests that were specific to field adaptation.     

Prism adaptation: The “target-pointing effect” as a function of exposure trials

The amount by which target pointing enhances prism adaptation (the “target-pointing effect”) was examined as a function of exposure trials. Each S served in three conditions—target-pointing, no-target, and control—wearing 20-diopter prism goggles in the first two. The S was measured prior to the exposure period on target-pointing accuracy with normal vision but with no visual feedback regarding his performance. Similar measures were taken after the 5th, 10th, 15th, 25th, 35th, 55th, and 95th exposure trials and after each of two consecutive 5-min postexposure periods in the dark. The two experimental conditions led to sharply rising and negatively accelerated adaptation (“negative aftereffect”) curves, the asymptotes of which differed markedly, in favor of the target-pointing condition. This difference in asymptotes indicates that the target-pointing effect is not limited to the early portion of the exposure period but, instead, is a relatively permanent phenomenon. There was no decline in adaptation during the postexposure period.     

Effects of situational cues on prism-induced aftereffects

A test was made of the hypothesis that external stimuli present during exposure to lateral displacement of the visual field can serve as situational cues whose presence or absence will influence the magnitude of aftereffects manifested subsequent to adaptation resulting from the exposure. The results indicated that the relative aftereffects were significantly greater when thenondisplacing goggles were worn during the periods in which aftereffect measurements were taken than was the case when they were removed during these test periods. The finding that manipulation of certain cues, i.e., the restriction of the visual field, weight, etc., of the goggles, associated with the adaptation period can in part determine the size of observed aftereffects provides evidence in support of the notion that aftereffects can be conditioned to precisely given constellations of stimuli In addition, the need for caution in conceptualizing aftereffects as simply the persistence of adaptive shifts once visual displacement has been terminated is suggested.     

Cognitive Load and Prism Adaptation

Subjects wore goggles with prisms that laterally displaced the visual field (rightward by 11.4°) and with full view of the limb engaged in paced (2-s rate) sagittal pointing at either an implicit (“straight ahead of the nose”) target (Experiment 1) or an explicit (positioned leftward by 11.4°) target (in Experiment 2). In experimental conditions, subjects performed a secondary cognitive task (mental arithmetic) simultaneously during target pointing. In control conditions, no cognitive load was imposed. Aftereffect measures of adaptation to the prismatic displacement were not substantially different when problem solving was required, but terminal error of the exposure pointing task was reliably affected by cognitive load. These results are consistent with the hypothesis of separable mechanisms for adaptive coordination and adaptive alignment. Adaptive coordination may be mediated by strategically flexible coordinative linkage between sensory–motor systems (eye–head and hand—head), but spatial alignment seems to be mediated by adaptive encoders within coordinatively linked subsystems. If the coordination task involves predominately automatic processing, coordinative linkage can be frequent enough under cognitive load for substantial realignment to occur even though exposure performance (adaptive coordination) may be less than optimal.     

Cognitive Load and Prism Adaptation

Subjects wore goggles with prisms that laterally displaced the visual field (rightward by 11.4 degree) and with full view of the limb engaged in paced (2-s rate) sagittal pointing at either an implicit ("straight ahead of the nose") target (Experiment 1) or an explicit (positioned leftward by 11.4 degree) target (in Experiment 2). In experimental conditions, subjects performed a secondary cognitive task (mental arithmetic) simultaneously during target pointing. In control conditions, no cognitive load was imposed. Aftereffect measures of adaptation to the prismatic displacement were not substantially different when problem solving was required, but terminal error of the exposure pointing task was reliably affected by cognitive load. These results are consistent with the hypothesis of separable mechanisms for adaptive coordination and adaptive alignment. Adaptive coordination may be mediated by strategically flexible coordinative linkage between sensory motor systems (eye-head and hand-head), but spatial alignment seems to be mediated by adaptive encoders within coordinatively linked subsystems. If the coordination task involves predominately automatic processing, coordinative linkage can be frequent enough under cognitive load for substantial realignment to occur even though exposure performance (adaptive coordination) may be less than optimal.     

Effects of Pointing Rate and Availability of Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation

While looking through laterally displacing prisms, subjects pointed 60 times straight ahead of their nose at a rate of one complete movement every 2 or 3 s, with visual feedback available early in the pointing movement or delayed until the end of the movement. Sagittal pointing was paced such that movement speed covaried with pointing rate. Aftereffect measures (obtained after every 10 pointing trials) showed that when the limb became visible early in a pointing movement, proprioceptive adaptation was greater than visual, but when visual feedback was delayed until the end of the movement, the reverse was true. This effect occurred only with the 3-s pointing rate, however. With the 2-s pointing rate, adaptation was predominately proprioceptive in nature, regardless of feedback availability. Independent of the availability of visual feedback, visual adaptation developed more quickly with 3-s pointing, whereas proprioceptive adaptation developed more rapidly with 2-s pointing. These results are discussed in terms of a model of perceptual-motor organization in which the direction of coordinative (guidance) linkage between eye-head (visual) and hand-head (proprioceptive) systems (and consequently the locus of discordance registration and adaptive recalibration) is determined jointly by pointing rate and feedback availability. An additional effect of pointing rate is to determine the rate of discordant inputs. Maximal adaptive recalibration occurs when the input (pointing) rate matches the time constant of the adaptive encoder in the guided system.     

Qualitative analyses of critical aspects of adaptation to the visually left-right reversed world

In this article, mechanisms of perceptual adaptation to the transposed world are analyzed based on introspective and behavioral performance data gathered during an extended period of wearing left-right reversing goggles. Three aspects central to this study were the mental map of the living space surrounding the subject, body image (both seen and felt), and the sensorimotor coordination system, which reflects the relationship between the subject and surroundings. These were investigated through map-drawing tests, self-representation tests when postures other than face forward were adopted, and after effects observed immediately after removal of the reversing goggles. It was concluded that the main course of the perceptual adaptation to the visually left-right reversed world consists of double reversals of the mental map and body image as well as the establishment of a new sensorimotor coordination system. In sharp contrast to the proprioceptive-change hypothesis, the importance of the visual nature of the body image was emphasized.     

Generalization of prism adaptation

Prism exposure produces 2 kinds of adaptive response. Recalibration is ordinary strategic remapping of spatially coded movement commands to rapidly reduce performance error. Realignment is the extraordinary process of transforming spatial maps to bring the origins of coordinate systems into correspondence. Realignment occurs when spatial discordance signals noncorrespondence between spatial maps. In Experiment 1, generalization of recalibration aftereffects from prism exposure to postexposure depended upon the similarity of target pointing limb postures. Realignment aftereffects generalized to the spatial maps involved in exposure. In Experiment 2, the 2 kinds of aftereffects were measured for 3 test positions, one of which was the exposure training position. Recalibration aftereffects generalized nonlinearly, while realignment aftereffects generalized linearly, replicating Bedford (1989, 1993a) using a more familiar prism adaptation paradigm. Recalibration and realignment require methods for distinguishing their relative contribution to prism adaptation.     

Dissociating proportion congruent and conflict adaptation effects in a Simon–Stroop procedure

Proportion congruent and conflict adaptation are two well known effects associated with cognitive control. A critical open question is whether they reflect the same or separate cognitive control mechanisms. In this experiment, in a training phase we introduced a proportion congruency manipulation for one conflict type (i.e. Simon), whereas in pre-training and post-training phases two conflict types (e.g. Simon and Spatial Stroop) were displayed with the same incongruent-to-congruent ratio. The results supported the sustained nature of the proportion congruent effect, as it transferred from the training to the post-training phase. Furthermore, this transfer generalized to both conflict types. By contrast, the conflict adaptation effect was specific to conflict type, as it was only observed when the same conflict type (either Simon or Stroop) was presented on two consecutive trials (no effect was observed on conflict type alternation trials). Results are interpreted as supporting the reactive and proactive control mechanisms distinction.     

Visual and proprioceptive adaptation to altered oculomotor adjustments

Adaptation to spectacles that alter in equivalent amounts the accommodation and the convergence with which objects are viewed was produced under two conditions. In one, S alternately pushed away or pulled toward him a screen that exhibited only a single vertical contour while wearing glaaaes that caused decreases in accommodation and convergence equivalent to 1.5 lens diopters. Here kinesthesis for these arm movements provided the only veridical distance cues, A small, but highly significant, adaptation effect was obtained with a teat in which S, before and after the adaptation period, pointed to the location of a test line in the distance dimension. Corresponding tests consisting in size and in depth estimates did not show an adaptation effect. In the other condition of adaptation, S moved objects by hand toward and away from himself while wearing spectacles that increased accommodation and convergence by the equivalent of 1.5 lens diopters. In addition to the altered oculomotor cues, some veridical visual cues for distance such as are caused by perspective were present. This condition yielded changes in size and depth estimates indicative of an adaptation in visual distance perception and a larger effect of adaptation measured by the pointing test. We concluded that the excess of the adaptation effect measured by pointing over that measured by size estimation represents an adaptation in proprioception, as did the pointing effect produced by our first adaptation condition.     

Preexposure pointing frequency effects on adaptation to prismatic viewing

The effect of frequency of preexposure pointing was studied to delermine its effect on subsequent adaptation to a prismatic exposure. Results showed that when Ss pointed equally to each target in a preexposure pointing task, adaptation was found to be greatest for the target on S’s prismatically shifted visual field periphery. However, when Ss pointed more frequently in the preexposure condition to a more central targe:, adaptation was geatest for this target.     

Target and arm observation effects on adaptation to prism displacement

Adaptation to displacement of objects in the visual field was studied as a function of preexposure test targets being absent or present in that field and lateral arm movement requiring no pointing at targets being observed or unobservable during prism exposure. Significantly greater adaptation was found when targets present during prism exposure were the same as those present during pre and postexposure test conditions. In addition, greater adaptation was found when S was permitted observation of lateral arm movement during prism exposure. Greatest adaptation was produced when both targets were present and arm movement was observable during prism exposure. In addition, when three targets were present during prism exposure, the greatest amount of adaptation was found for targets on S’s prismatically shifted visual field periphery.     

Adaptation to prism-displaced vision: The importance of target-pointing

Two experiments investigated the hypothesis that the experience of manually pointing at visual targets enhances motoric adaptation to prism-displaced vision. Experiment 1 indicated that when adaptation was measured by means of redirected pointing behavior (negative aftereffect) it varied directly with the specificity of the target, the least adaptation occurring when no target was available. This relationship was not observed when adaptation was measured in terms of a shift in the felt position of the prism-exposed hand (proprioceptive shift). Experiment 2 demonstrated that after double the prism-exposure trials used in Experiment 1, target-pointing experience continued to enhance adaptation (as indexed by both types of adaptation measure). In both experiments negative aftereffect was significantly larger than proprioceptive shift for all experimental conditions and the two measures were not correlated. These latter two findings cast doubt on Harris’s notion that negative aftereffect is entirely the result of altered position sense.     

Prism adaptation in alternately exposed hands

We assessed intermanual transfer of the proprioceptive realignment aftereffects of prism adaptation in right-handers by examining alternate target pointing with the two hands for 40 successive trials, 20 with each hand. Adaptation for the right hand was not different as a function of exposure sequence order or postexposure test order, in contrast with adaptation for the left hand. Adaptation was greater for the left hand when the right hand started the alternate pointing than when the sequence of target-pointing movements started with the left hand. Also, the largest left-hand adaptation appeared when that hand was tested first after exposure. Terminal error during exposure varied in cycles for the two hands, converging on zero when the right hand led, but no difference appeared between the two hands when the left hand led. These results suggest that transfer of proprioceptive realignment occurs from the right to the left hand during both exposure and postexposure testing. Such transfer reflects the process of maintaining spatial alignment between the two hands. Normally, the left hand appears to be calibrated with the right-hand spatial map, and when the two hands are misaligned, the left-hand spatial map is realigned with the right-hand spatial map.     

Driving at night with a cataract: Risk homeostasis?

Driving with a cataract can be dangerous, especially at night when road lighting and automotive lighting produce glare. Disability glare alters visual performance, while discomfort glare contributes to restricted mobility, with drivers avoiding driving at night. The present study was focused on the visual effects of an early cataract, and aimed at comparing three driving performance indexes at night, under glare conditions, with and without a simulated cataract. Two indexes directly referred to road safety, while a measure could be related to behavioral adaptation.Using a driving simulator, twenty-six participants were asked to drive in simulated night-time conditions, under controlled photometric conditions where the adaptation luminance and the glare level were consistent with a two-lane rural road at night with oncoming traffic. The visual effects of a bilateral cataract were simulated using goggles which were in the range of an early cataract in terms of light scattering, light transmission, visual acuity and contrast sensitivity loss. Participants were asked to avoid virtual pedestrians on the road, both with and without a simulated cataract. Three performance indexes were considered: the rate of pedestrian crashes, the distance to the pedestrian when the participant avoided the crash, and the mean speed, which allowed to control for a possible behavioral adaptation to the reduced visual performance. For a better understanding of the visual functions responsible for the degraded driving behavior, contrast sensitivity and time-to-collision performance were also measured in glare conditions.While simulated cataract resulted in slightly slower speeds, poorer driving performance was observed with the goggles than without, with more pedestrians being hit and shorter stopping distances. Time-to-collision estimates at 90 km/h were found to be predictive of stopping distances with a simulated cataract, while contrast sensitivity in glare conditions at 13 cycles per degree was found to be associated with the occurrence of a crash with cataract.The decrease in speed with a simulated cataract was real but ineffective in terms of driving safety, which suggests that the behavioral adaptation to the degraded visual performance was insufficient. The precise impact of a cataract on driving abilities remains to be further studied, to provide scientific knowledge to help practitioners determine the moment when the individuals should forego driving.     

Presentation- and test-trial effects on acquisition and retention of distance and location

Acquisition and retention effects of presentation and test trials on movement distance (Experiment 1) and location (Experiment 2) were examined under three multitrial training methods. Three groups of 15 government employees performed three training trial cycles consisting of six trials each. Training methods emphasized either presentation-trial repetition, test-trial repetition, or presentation- and test-trial alternation within cycles. After training, both short- (3 min.) and long-term (24 hr.) retention scores were recorded. Absolute error revealed that (a) presentation-trial repetition promoted acquisition of both distance and location but resulted in extensive short- and long-term forgetting; (b) test-trial repetition produced error increases within cycles, potentiated presentation-trial effectiveness during acquisition, and enhanced long-term retention of both distance and location; (c) presentation- and test-trial alternation promoted distance and location acquisition and produced distance retention intermediate to that of the other two methods. Experiment 3 provided data to support the interpretation that test-trial retention benefits are a function of movement execution mode.