Mike Tucker

The potentiation of grasp types during visual object categorization

The close integration between visual and motor processes suggests that some visuomotor transformations may proceed automatically and to an extent that permits observable effects on subsequent actions. A series of experiments investigated the effects of visual objects on motor responses during a categorisation task. In Experiment 1 participants responded according to an objects natural or manufactured category. The responses consisted in uni-manual precision or power grasps that could be compatible or incompatible with the viewed object. The data indicate that object grasp compatibility significantly affected participant response times and that this did not depend upon the object being viewed within the reaching space. The time course of this effect was investigated in Experiments 2–4b by using a go-nogo paradigm with responses cued by tones and go-nogo trials cued by object category. The compatibility effect was not present under advance response cueing and rapidly diminished following object extinction. A final experiment established that the compatibility effect did not depend on a within-hand response choice, but was at least as great with bi-manual responses where a full power grasp could be used. Distributional analyses suggest that the effect is not subject to rapid decay but increases linearly with RT whilst the object remains visible. The data are consistent with the view that components of the actions an object affords are integral to its representation.

Micro-affordance: The potentiation of components of action by seen objects

It is suggested that seen objects potentiate a range of actions associated with them, irrespective of the intentions of the viewer. Evidence for this possibility is provided by the data from two experiments, both of which required a participant to make a binary motor response to an auditory stimulus. In the first experiment the response was a power or precision grip, which was performed whilst simultaneously viewing a real object which would normally be grasped using either a power or precision grip. A significant interaction of response and grip compatibility of the object was observed. Similar results were obtained in the second experiment when a wrist rotation of a given direction was used as a response, whilst viewing objects which would require wrist rotations if they were to be grasped. The effects of the seen objects on components of action are described as microaffordances which are said to be dispositional states of the viewers nervous system.

Dissociating object-based and space-based affordances

In what we term the orientation effect, faster spatial responses are made to the corresponding task irrelevant orientation of an object. We ask how this effect relates to object affordances, how attention may be involved, and how the effect relates to the better understood Simon effect. Two separate stimulus-response compatibility effects (an orientation effect and a Simon effect) were observed when spatial responses were made to photographs of objects whose orientation and location had been simultaneously manipulated. When attentional demands were high these separate effects were found using hand responses and foot responses, suggesting an abstract rather than specific coding of object affordances. However, when attentional demands were low only the Simon effect was observed, suggesting that, in order to obtain the orientation effect, objects must be represented at the level of an object.

Grasp preparation improves change detection for congruent objects.

A series of experiments provided converging support for the hypothesis that action preparation biases selective attention to action-congruent object features. When visual transients are masked in so-called change-blindness scenes, viewers are blind to substantial changes between 2 otherwise identical pictures that flick back and forth. The authors report data in which participants planned a grasp prior to the onset of a change-blindness scene in which 1 of 12 objects changed identity. Change blindness was substantially reduced for grasp-congruent objects (e.g., planning a whole-hand grasp reduced change blindness to a changing apple). A series of follow-up experiments ruled out an alternative explanation that this reduction had resulted from a labeling or strategizing of responses and provided converging support that the effect genuinely arose from grasp planning.

The role of visual attention in action priming

It has been demonstrated that the task-irrelevant left–right orientation of an object is capable of facilitating left–right-hand responses when the object is orientated towards the responding hand. We investigated the role of attention in this orientation effect. Experiment 1 showed that object orientation facilitates responses of the hand that is compatible with the objects orientation, despite the entire object being irrelevant. However, when a task-relevant fixation point was displayed over the prime object in Experiment 2, the effect was not observed. Together Experiments 1 and 2 suggest that the orientation information of viewed objects primes the action selection processes even when the object is irrelevant, but only when attention is not allocated to a competing stimulus during the prime presentation. Experiment 3 suggested that the elimination of the effect in Experiment 2 could not be attributed to the elimination of an attentional shift to the graspable part of the prime. Finally, Experiment 4 showed that object orientation can evoke an abstract response code, influencing the selection of finger responses.

Does Selecting One Visual Object From Several Require Inhibition of the Actions Associated With Nonselected Objects

Four experiments are described in which 1 visual object (the target) was selected from another (the distractor) according to its color (Experiments 1, 2, and 4) or its relative location (Experiment 3) and then was classified according to a simple geometric property. Object classification was signaled as fast as possible by a precision or power grip response, and this grip was either compatible or incompatible with either object. When targets were selected by color, target-compatible grip responses were facilitated, but distractor-compatible grip responses were impaired. When targets were selected by location, similar results were obtained for target-compatible grip responses, but not distractor-compatible grip responses. These data are explained in terms of the involvement of action codes in object-level selection.

Precision and power grip priming by observed grasping

The coupling of hand grasping stimuli and the subsequent grasp execution was explored in normal participants. Participants were asked to respond with their right- or left-hand to the accuracy of an observed (dynamic) grasp while they were holding precision or power grasp response devices in their hands (e.g., precision device/right-hand; power device/left-hand). The observed hand was making either accurate or inaccurate precision or power grasps and participants signalled the accuracy of the observed grip by making one or other response depending on instructions. Responses were made faster when they matched the observed grip type. The two grasp types differed in their sensitivity to the end-state (i.e., accuracy) of the observed grip. The end-state influenced the power grasp congruency effect more than the precision grasp effect when the observed hand was performing the grasp without any goal object (Experiments 1 and 2). However, the end-state also influenced the precision grip congruency effect (Experiment 3) when the action was object-directed. The data are interpreted as behavioural evidence of the automatic imitation coding of the observed actions. The study suggests that, in goal-oriented imitation coding, the context of an action (e.g., being object-directed) is more important factor in coding precision grips than power grips.

Bodies and other visual objects: the dialectics of reaching toward objects

Participants viewed video clips of a left or right-handed reach toward an object that was orientated with a handle to the left or right. They were required to classify the object by making a left or right-handed key-press and ignore the reach. These responses were, never-the-less, affected by the observed reach in ways which largely reflected the opportunities for complementary actions in the viewed scenes, given the simultaneous constraints of the object orientation combined with the direction and hand of reach. These influences are claimed to reflect the interdependency of the action possibilities that arise from a set of objects and agents in three-dimensional space that together determine behaviour.

Manual asymmetries in visually primed grasping

Previous research has shown that the task irrelevant size of familiar objects facilitates compatible precision and power grip responses. The present study examined whether the task irrelevant size of novel objects produces the same compatibility effect. However, the main objective of the study was to investigate whether visually primed precision and power grips are manually asymmetric. Experiment 1 showed that the size of a novel prime object does facilitate compatible precision and power grips, even when both the object itself and the grasp type are irrelevant to the current task. However, this effect was only found when the precision grip was made with the right hand (RH) and the power grip was made with the left hand (LH). When these grips were made with the opposite hands, the effect was absent. Experiment 2 replicated the LH bias for large objects and the RH bias for small objects when power and precision grip responses were replaced with simple LH and RH button-press responses. It appears that the two hemispheres are specialised with regard to precision and power compatible objects.

When motor attention improves selective attention: The dissociating role of saliency

There is evidence that preparing and maintaining a motor plan (“motor attention”) can bias visual selective attention. For example, a motor attended grasp biases visual attention to select appropriately graspable object features (Symes, Tucker, Ellis, Vainio, & Ottoboni, 2008). According to the biased competition model of selective attention, the relative weightings of stimulus-driven and goal-directed factors determine selection. The current study investigated how the goal-directed bias of motor attention might operate when the stimulus-driven salience of the target was varied. Using a change detection task, two almost identical photographed scenes of simplistic graspable objects were presented flickering back and forth. The target object changed visually, and this change was either high or low salience. Target salience determined whether or not the motor attended grasp significantly biased visual selective attention. Specifically, motor attention only had a reliable influence on target detection times when the visual salience of the target was low.