Biomedical subjects

Liana E Brown

Publications and source records attributed to Liana E Brown.

4 recordsLinked to original sources

PubMed2005

Peripheral vision for perception and action.

Anatomical and physiological evidence suggests that vision-for-perception and vision-for-action may be differently sensitive to increasingly peripheral stimuli, and to stimuli in the upper and lower visual fields (VF). We asked participants to fixate one of 24 randomly presented LED arranged radially in eight directions and at three eccentricities around a central target location. One of two (small, large) target objects was presented briefly, and participants responded in two ways. For the action task, they reached for and grasped the target. For the perception task, they estimated target height by adjusting thumb-finger separation. In a final set of trials for each task, participants knew that target size would remain constant. We found that peak aperture increased with eccentricity for grasping, but not for perceptual estimations of size. In addition, peak grip aperture, but not size-estimation aperture, was more variable when targets were viewed in the upper as opposed to the lower VF. A second experiment demonstrated that prior knowledge about object size significantly reduced the variability of perceptual estimates, but had no effect on the variability of grip aperture. Overall, these results support the claim that peripheral VF stimuli are processed differently for perception and action. Moreover, they support the idea that the lower VF is specialized for the control of manual prehension. Finally, the effect of prior knowledge about target size on performance substantiates claims that perception is more tightly linked to memory systems than action.

Adult↗

PubMed2003

Movement speed effects on limb position drift.

Previous research has shown that even when limb position drifts considerably during continuous blind performance, the topological and metrical properties of generated hand paths remain remarkably invariant. We tested two possible accounts of this intriguing effect. According to one hypothesis, position drift is due to degradation of limb-position information. This hypothesis predicted that drift of static hand positions at movement reversals should not depend on movement speed. According to the other hypothesis, position drift is due to degradation of movement information. This hypothesis predicted that drift of static hand positions at movement reversals should vary with movement speed. We tested these two hypotheses by varying the required movement speed when normal human adults performed back-and-forth manual positioning movements in the absence of visual feedback. Movement distance and direction were well preserved even though hand positions between movements drifted considerably. In accord with the movement error hypothesis, but not in accord with the position hypothesis, the rate at which hand positions drifted depended on movement speed. The data are consistent with the idea that hand position, which defines the origin of the trajectory control coordinate system, and movement trajectory are controlled by distinct neural mechanisms.

Adult↗

PubMed2003

Limb position drift: implications for control of posture and movement.

In the absence of visual feedback, subject reports of hand location tend to drift over time. Such drift has been attributed to a gradual reduction in the usefulness of proprioception to signal limb position. If this account is correct, drift should degrade the accuracy of movement distance and direction over a series of movements made without visual feedback. To test this hypothesis, we asked participants to perform six series of 75 repetitive movements from a visible start location to a visible target, in time with a regular, audible tone. Fingertip position feedback was given by a cursor during the first five trials in the series. Feedback was then removed, and participants were to continue on pace for the next 70 trials. Movements were made in two directions (30 degrees and 120 degrees ) from each of three start locations (initial shoulder angles of 30 degrees, 40 degrees, 50 degrees, and initial elbow angles of 90 degrees ). Over the 70 trials, the start location of each movement drifted, on average, 8 cm away from the initial start location. This drift varied systematically with movement direction, indicating that drift is related to movement production. However, despite these dramatic changes in hand position and joint configuration, movement distance and direction remained relatively constant. Inverse dynamics analysis revealed that movement preservation was accompanied by substantial modification of joint muscle torque. These results suggest that proprioception continues to be a reliable source of limb position information after prolonged time without vision, but that this information is used differently for maintaining limb position and for specifying movement trajectory.

Adult↗

PubMed2002

Feature-specific perceptual processing dissociates action from recognition.

Does visual processing differ for action and recognition? To address this question, the authors capitalized on research showing that color is preferred over binocular disparity in the ventral (recognition) stream, whereas disparity is preferred over color in the dorsal (action) stream. Participants searched for oblique targets among vertical distractors in displays defined only by color or disparity. Action-task participants stamped the target with a handheld block, whereas recognition-task participants lifted the block through a target-compatible gap. Analyses of reaction time and time-varying hand orientation showed that disparity and color displays were processed equally efficiently during action, but disparity was processed less efficiently than color during recognition. The results suggest that visual processing differs for action and recognition.

Adolescent↗