Spatial orientation of a limb using egocentric reference points

Testing the hypothesis that spatial localization can be based on an abstracted spatial location code, rather than on stored proprioceptive information, orientation of an unseen limb was contrasted under intra- and interlimb-movement conditions. In Experiment 1, movements were executed in the midline either vertically upward or horizontally forward in the sagittal plane. These results revealed that intralimb errors were smaller than interlimb errors only at the most distant criterion spatial targets, and it was hypothesized that positioning of a limb could be mediated by a spatial location code if spatial targets were coded in association with body reference points. Experiment 2 tested the egocentric referent hypothesis further by manipulating the availability of body-based spatial reference points under intra- and interlimb conditions. At spatial targets that could be coded in conjunction with body reference points, no difference was found between intra- and interlimb accuracy. In contrast, at spatial targets where body reference points were absent, or at least made difficult to rely on, accuracy was greater in the intralimb condition. It was concluded that spatial reference points, in this instance body-based, are necessary if the spatial positioning of a limb is to be based on the spatial location code. The data were also discussed within a more comprehensive framework of spatial frames of reference.     

The patterns of silence: Performance structures in sentence production

The pauses produced by speakers while reading familiar material were used to obtain hierarchical sentence structures. Identical structures were obtained from parsing, indicating that the performance structures of sentences are not task specific. The linguistic surface structure of a sentence is a good predictor of the pause durations. However, speakers also revealed a tendency to place pauses between segments of equal length. A simple cyclical model combining, for each pause location, an index of linguistic complexity and a measure of the distance to the midpoint of the segment, accounts for 72% of the pause time variance as opposed to 56% for the linguistic index alone. The generality of the model is shown by its good prediction of the pause durations obtained in unrelated studies in English and American Sign Language.     

Cerebral asymmetry for American Sign Language: The effects of moving stimuli

Previous studies of cerebral asymmetry for the perception of American Sign Language (ASL) have used only static representations of signs; in this study we present moving signs. Congenitally deaf, native ASL signers identified moving signs, static representations of signs, and English words. The stimuli were presented rapidly by motion picture to each visual hemifield. Normally hearing English speakers also identified the English words. Consistent with previous findings, both the deaf and the hearing subjects showed a left-hemisphere advantage to the English words; likewise, the deaf subjects showed a right hemisphere advantage to the statically presented signs. With the moving signs, the deaf showed no lateral asymmetry. The shift from right dominance to a more balanced hemispheric involvement with the change from static to moving signs is consistent with Kimura's position that the left hemisphere predominates in the analysis of skilled motor sequencing (Kimura 1976). The results also indicate that ASL may be more bilaterally represented than is English and that the spatial component of language stimuli can greatly influence lateral asymmetries.     

Gradients of auditory generalization for blind, retarded children

Severely retarded, blind children were conditioned to respond differentially to two intensities of a pure tone. Gradients of auditory generalization were obtained that were reliable and similar to those for normal adults, but often asymmetric and non-monotonic.     

Comorbid anxiety and mood disorders among persons with social anxiety disorder.

Axis I comorbidity is associated with greater severity of social anxiety disorder. However, the differential effects of comorbid mood and anxiety disorders on symptom severity or treatment outcome have not been investigated. We evaluated 69 persons with uncomplicated social anxiety disorder, 39 persons with an additional anxiety disorder, and 33 persons with an additional mood disorder (with or without additional anxiety disorders). Those with comorbid mood disorders reported greater duration of social anxiety than those with uncomplicated social anxiety disorder. They were also judged, before and after 12 weeks of cognitive-behavioral group treatment and at follow-up, to be more severely impaired than those with no comorbid diagnosis. In contrast, persons with comorbid anxiety disorders were rated as more impaired than those with no comorbid diagnosis on only a single measure. Type of comorbid diagnosis did not result in differential rates of improvement of social anxiety disorder.     

Assessing Client Progress Session by Session in the Treatment of Social Anxiety Disorder: The Social Anxiety Session Change Index

Frequent assessment during therapy can improve treatments and provide accountability. However, clinicians often do not monitor progress because of the time it takes to administer and score assessments. In response, the Social Anxiety Session Change Index (SASCI) was developed. The SASCI is a short, easily administered rating of subjective improvement that asks clients with social anxiety disorder how much they have changed since the beginning of therapy. Change on the SASCI was related to change in fear of negative evaluation, a core aspect of social anxiety, and to clinician-rated improvement, but not to ratings of anxiety sensitivity or depression. Because it is brief and easily interpretable, the SASCI can be used in a variety of clinical settings to monitor change across therapy. The SASCI is presented along with examples of how the information gathered from frequent administration can inform clinical practice.     

The effect of Parkinson's disease on the control of multi-segmental coordination

An experiment was designed to test whether or not Parkinson's disease (PD) patients were able to maintain endpoint kinematic patterns in a prehension task involving movement of the torso. Nine PD patients and nine healthy controls were asked to reach for and grasp a full cup of water that was either covered or uncovered and placed beyond the reach of the outstretched arm. An OPTOTRAK (Northern Digital) 3-dimensional motion analysis system was used to capture the movement of four markers placed on the arm, hand, and torso. The results indicated the Parkinson's patients had a decreased ability to maintain the kinematics of the end effector. The PD patients were also found to be impaired in terms of their ability to synchronize the arm, hand, and torso. More specifically, although the elderly controls seemed to employ a strategy of increasing the involvement of the torso when reaching to grasp the uncovered cup, no such strategy was observed in the PD patients. Collectively, the results suggest that the multi-joint synergies observed in the elderly controls, which help preserve relatively consistent endpoint trajectories, are disrupted in Parkinson's patients.     

Stereoillusory motion concomitant with lateral head movements

Stationary objects in a stereogram can appear to move when viewed with lateral head movements. This illusory motion can be explained by the motion-distance invariance hypothesis, which states that illusory motion covaries with perceived depth in accordance with the geometric relationship between the position of the stereo stimuli and the head. We examined two predictions based on the hypothesis. In Experiment 1, illusory motion was studied while varying the magnitude of binocular disparity and the magnitude of lateral head movement, holding viewing distance constant. In Experiment 2, illusory motion was studied while varying binocular disparity and viewing distance, holding magnitude of head movement constant. Ancillary measures of perceived depth, perceived viewing distance, and perceived magnitude of lateral head movement were also obtained. The results from the two experiments show that the extent of illusory motion varies as a function of perceived depth, supporting the motion-distance invariance hypothesis. The results also show that the extent of illusory motion is close to that predicted from the geometry in crossed disparity conditions, whereas it is greater than the predicted motion in uncrossed disparity conditions. Furthermore, predictions based on perceptual variables were no more accurate than predictions based on geometry.     

Error Detection and Correction in a Structured Movement Task

Error-detection and error-correction experiments were conducted to examine the assumption that organizational processes play an important role in motor learning and control. During the initial phase of each experiment, the sensory aspects of five movements were held constant while the organizational structure (sequential vs. random) of the movements was varied. In the learning phase of both experiments, the effect of organization produced increased reproduction accuracy for the structured movement sequences compared to those that were random. This benefit of organization carried over into the error detection and correction parts of the experiments where it was shown that improved error detection and correction capabilities were assisted by the manner in which the movements were presented. The importance of cognitive processes is discussed in terms of past and contemporary accounts of motor learning and control.