Louise A. Howard

Selective Reaching to Grasp: Evidence for Distractor Interference Effects

Transport and grasp kinematics were examined in a task in which subjects selectively reached to grasp a target object in the presence of non-target objects. In a variety of experiments significant interference effects were observed in temporal parameters, such as movement time, and spatial parameters, such as path. In general, the presence of non-targets slowed down the reach. Furthermore, reach paths were affected such that the hand veered away from near non-targets in reaches for far targets, even though the non-targets were not physical obstacles to the reaching hand. In contrast, the hand veered towards far non-targets in near reaches. We conclude that non-targets evoke competing responses, and the inhibitory mechanisms that resolve this competition are revealed in the reach path.

Vision influences tactile perception without proprioceptive orienting

THE perception of tactile stimuli is facilitated when subjects look towards the stimulated body site: this facilitation even takes place when visual information is unavailable, as when orienting in the dark. It is not known whether the facilitation is due entirely to such proprioceptive orienting of eye and head, or whether visual information of the body site can also facilitate touch. An experiment is reported which dissociates vision and proprioception, and demonstrates for the first time that vision of a body part, independent of proprioceptive orienting, can indeed effect somatosensation.

Hand deviations away from visual cues: Indirect evidence for inhibition

Previous research has demonstrated that when a stimulus is to be ignored, the path of motion towards a target (saccade or manual reach) deviates away from the to-be-ignored stimulus. Path deviations in saccade and reaching tasks have, however, been observed in very different situations. In the saccade tasks subjects initially attended to a cue, then disengaged attention while saccading to a target. By contrast, in the selective reaching tasks attention was continuously withdrawn from the to-be-ignored stimulus, as this was irrelevant throughout the experiment. In the two experiments reported here, cues similar to those studied in saccade tasks are examined with selective reaching procedures. Experiment 1 shows that when a coloured light-emitting diode cue, upon which subjects engage and then subsequently disengage attention, is close to the responding hand, the hand deviates away from the cue. Experiment 2 confirms this cue avoidance by showing that, compared with central fixation alone, the hand veers away from a central cue. These results confirm that the path deviations observed in saccades can also be obtained in manual reaching movements. Such findings support the notion that eye and hand movements are both affected by inhibitory mechanisms of attention.

Reaching affects saccade trajectories.

Abstract. The pre-motor theory suggests that, when attention is oriented to a location, the motor systems that are involved in achieving current behavioural goals are activated. For example, when a task requires accurate reaching, attention to a location activates the motor circuits controlling saccades and manual reaches. These actions involve separate neural systems for the control of eye and hand, but we believe that the selection processes acting on neural population codes within these systems are similar and can affect each other. The attentional effect can be revealed in the subsequent movement. The present study shows that the path the eye takes as it saccades to a target is affected by whether a reach to the target is also produced. This effect is interpreted as the influence of a hand-centred frame used in reaching on the spatial frame of reference required for the saccade.

Action-centred negative priming: Evidence for reactive inhibition

Experiments are described in which the spatial relationship between a stimulus and respondent is held constant in terms of visual and body-centred coordinates, while the complexity of the response is manipulated. It is demonstrated that the degree of complexity of an action directed to the same spatial location determines the level of negative priming observed. This result supports the notions that (1) inhibitory selection mechanisms act on action-centred representations, and (2) the level of inhibition is reactive to the relative potency of the evoked action. The results are also discussed in terms of alternative explanations of negative priming. It is concluded that the results are inconsistent with theories that do not involve inhibitory selection mechanisms.

Inhibition of return in a selective reaching task: an investigation of reference frames.

Most previous studies of inhibition of return (IOR) have examined reaction time (RT) and accuracy. These effects have been observed via saccades to targets or with key-press responses. In this study the authors examined, for the first time, IOR in components of a selective reaching task in which participants directly reached for and depressed target keys. When the interval between cue and target was 600 ms, robust IOR effects were observed in RT to begin the reach, but no effects were observed in the movement components (movement time to complete the reach and the path of the reach). However, when the cue-target interval was short (200 ms), hand paths deviated toward the cue. The results suggest that although RT measures of IOR appear to reveal perceptual rather than action-based processes, action-based representations may be briefly activated by irrelevant cues, which can be observed via analysis of three-dimensional reach path.

A Rapid Effect of Caffeinated Beverages on Two Choice Reaction Time Tasks

Abstract Though consumers of tea and coffee can report feeling beneficial subjective effects of consumption virtually immediately, tests for objective effects of caffeine immediately post-consumption have been rare. Two experiments examined caffeines ability to influence reaction time in choice reaction time tasks, using a dose of caffeine typical of a cup of tea or instant coffee, and testing at short post-consumption delays. Two groups of participants were given 60 mg of caffeine, after overnight abstinence, either in a hot tea drink, or a hot water drink. Two control groups also received hot tea or water, but without caffeine. In Experiment 1, participants were given a keypress task before the drink (baseline), immediately after the drink, and 40 min after the drink. In Experiment 2, a touch-screen test was given either 1, 14, or 27 min post consumption. Caffeine was found to reduce the effect of a distracter on reaction time in the keypress test and to reduce reaction time in a component of the touch-screen task; however, in neither experiment were these effects significantly modulated by post-consumption delay length. Thus, the speed of caffeines action on psychomotor performance was shown to be on the order of minutes.

Mechanisms of attention in touch

A series of experiments demonstrated the role of higher level cognitive processes, such as attention, in tactile perception. The first series of experiments demonstrated that automatic orienting to a tactile stimulus resulted in inhibition of subsequent stimuli at that body site--inhibition of return (IOR). A possible explanation suggests that inhibition of saccades to a body site can cause the inhibition of subsequent stimuli presented to that same site. In contrast, when the subjects strategically oriented attention to the stimulus, the processing of subsequent stimuli at that body site was facilitated. In both of these experiments the skin received exactly the same test stimuli, (100 Hz sine wave presented for 50 ms), but very different effects were observed depending upon attentional strategy. Experimental manipulations showed that this cannot be due to a peripheral masking of the receptors after cue presentation to the target. Rather the results may be explained centrally by cognitive, particularly attentional mechanisms. Cross-modal interactions suggest that tactile processes are facilitated when vision is oriented to the body site receiving stimulation. Possible explanations come from recent findings of spatiotopic maps of different sensory modalities in the superior colliculus of the midbrain and in the parietal lobe. These are integrated with motor systems that control saccades and head orientation towards sensory inputs. Excitatory links among these maps could be the source of the observed facilitation effects.