Sensorimotor responsiveness in rats with unilateral superior collicular and amygdaloid lesions.

Large unilateral lesions of superior colliculus, but not amygdala, result in strong ipsiversive progression tendencies and permanent neglects of visual, auditory, and whisker-touch stimuli presented on the contralateral side of the body. Combined collicular-amygdaloid lesions also yield circling behaviors and multimodal neglects that are completely independent of the order or laterality of the amygdaloid lesion. Rats with colliculectomy either neglect or else turn away from pinches of the contralateral ear and forepaw. Subjects with combined lesions display more crossed orientations, and this tendency is greatly potentiated by ipsilateral lesion placement. The nature and time course of the crossed response in rats with sensory neglects is reminiscent of the clinical syndrome described as alloaesthesia or as contralateral sensory displacement.     

Directional uncertainty in visually guided pointing

Studies of the relationship between stimulus-response uncertainty and reaction times indicate three qualitatively different functions: Hick's law, simple-choice step function, or flat curve (no effect at all). The extent of stimulus-response S-R) compatibility appears to interact with the effects of uncertainty on response times. One possible hypothesis regarding these various S-R uncertainty functions is that uncertainty will have an effect whenever the stimuli and their associated responses are not within the same egocentric spatial coordinates. We tested this hypothesis in 5 undergraduate participants (2 men, M age 18.7 yr., range 18-20) by investigating the time-course of pointing to peripherally located visual targets under four different levels of uncertainty (1, 2, 4, or 8 possible locations). Surprisingly, the resulting response function does not match any of those previously reported. Visually guided pointing produced a quadratic reaction time function as S-R uncertainty increases in log2 steps from 1 to 8.     

Implicit biases in visually guided action

For almost half a century dual-stream advocates have vigorously defended the view that there are two functionally specialized cortical streams of visual processing originating in the primary visual cortex: a ventral, perception-related ‘conscious’ stream and a dorsal, action-related ‘unconscious’ stream. They furthermore maintain that the perceptual and memory systems in the ventral stream are relatively shielded from the action system in the dorsal stream. In recent years, this view has come under scrutiny. Evidence points to two overlapping action pathways: a dorso-dorsal pathway that calculates features of the object to be acted on, and a ventro-dorsal pathway that transmits stored information about skilled object use from the ventral stream to the dorso-dorsal pathway. This evidence suggests that stored information may exert significantly more influence on visually guided action than hitherto assumed. I argue that this, in turn, supports the notion of skilled automatic action that is nonetheless agential. My focus here will be on actions influenced by implicit biases (stereotypes/prejudices). Action that is biased in this way, I argue, is in an important sense intentional and agential.

     

Asymmetries in the regulation of visually guided aiming

An experiment was conducted to examine the contribution of sensory information to asymmetries in manual aiming. Movements were performed in four vision conditions. In the full-vision condition (FV), subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off condition (AO), the room lights were extinguished at movement initiation, preventing vision of the moving limb. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. In a no-vision (NV) condition, ambient illumination was removed and the target was extinguished upon initiation of the response movement. Results indicated that accuracy was superior in the full-vision and target-off conditions and when movements were made by the right hand. Movements made by the right hand were also of shorter mean duration. The magnitudes of performance asymmetries were uninfluenced by vision condition. Analyses of movement kinematics revealed that movements made in conditions in which there was vision of the limb exhibited a greater number of discrete modifications of the movement trajectory. On an individual-trial basis, no relationship existed between accuracy and the occurrence of discrete modifications. These data suggest that although vision greatly enhances accuracy, discrete modifications subserved by vision reflect the imposition of nonfunctional zero-order control processes upon continuous higher-order control regimes.     

Cues and control strategies in visually guided tracking

Detailed quantitative models are required to investigate the neurological basis of motor behavior. Previous studies of visually guided manual tracking have either identified a variety of control signals (cues) for planning tracking movements or analyzed how a single cue is used (i.e., one-tracking strategy). A systematic, quantitative analysis of the effects and interactions of cues in terms of human manual-tracking performance is presented here together with measurements of concomitant eye movements. These measurements help define the routes by which information reaches the CNS, and the analysis elucidates how the control signals are processed and combined. The results quantify not only the large improvement in performance observed when the target waveform being tracked is predictable but also the extent to which this improvement depends on the availability of current information about target movements and positional error. Target information is shown to provide short-term prediction independent of the error signals used in on-line negative feedback control.