Is access to the body structural description sensitive to a body part's significance for action and cognition? A study of the sidedness effect using feet.

There is evidence suggesting that viewing hands triggers automatic access to the Body Structural Description, a visual-spatial representation of human body parts configuration. Hands, however, have a special representational status within the brain because of their significance for action and cognition. We tested whether feet, less important in gestural and object-directed action, would similarly show automatic access to the Body Structural Description. Positive evidence of that would be finding a Sidedness effect (Ottoboni et al. J Exp Psychol Hum Percept Perform 31:778-789, 2005), a Simon-like paradigm previously used to study automatic hand recognition. This effect demonstrates that processing hands generates spatial codes corresponding to the side of the body on which the hand would be located within the Body Structural Description map. Feet were shown with toes pointing upwards (Experiment 1), without any connection to the ankle and the leg (Experiment 2) and with toes pointing downwards (Experiment 3). Results revealed a Sidedness effect in both Experiments 1 and 3: spatial compatibility occurred according to the side of the body that each foot would assume within the Body Structural Description. In Experiment 2, as already found in stimuli similarly featured, no effect emerged, due to the lack of the necessary anatomical links connecting the foot to a body. Results suggest that body parts with variable degrees of significance for action and cognition can access automatically the Body Structural Description hence reinforcing the hypothesis of its pure visuo-spatial nature.

Integrating Action and Language through Biased Competition.

Several recent psychological investigations have demonstrated that planning an action biases visual processing. Symes et al. (2008) for example, reported faster target detection for a changing object amongst several non-changing objects following the planning of a target-congruent grasp. The current experimental work investigated how this effect might compare to, and indeed integrate with, effects of language cues. Firstly a cuing effect was established in its own right using the same change-detection scenes. Sentences cued object size (e.g., "Start looking for a change in the larger objects"), and these successfully enhanced detection of size-congruent targets. Having thereby established two effective sources of bias (i.e., action primes and language cues), the remaining three experiments explored their co-occurrence within the same task. Thus an action prime (participants planned a power or precision grasp) and a language cue (a sentence) preceded stimulus presentation. Based on the tenets of the biased competition model (Desimone and Duncan, 1995), various predictions were made concerning the integration of these different biases. All predictions were supported by the data, and these included reliably stronger effects of language, and concurrent biasing effects that were mutually suppressive and additive.

Hand processing depends on the implicit access to a spatially and bio-mechanically organized structural description of the body.

Recent evidence using a modified Simon task suggests that hand processing involves implicit coding of the spatial position of the hand relative to the side of the body to which it is attached from the viewer's reference point. This effect, called the Sidedness effect, has been found to emerge only when at least the forearm is present (the forearm thus providing the spatial reference for representing the rest of body) and it has been interpreted within the framework of the structural representation of the body. In this study we use the same modified Simon task to investigate whether hand processing involves the implicit access to a spatially and bio-mechanically organized structural body representation. In a first experiment the hand stimuli were attached to a body inappropriately without respecting the bio-mechanical constraints and no Sidedness effect was found. In Experiment 2 where the hand stimuli were presented attached to a non-bodily shape the Sidedness effect was observed only when they were attached appropriately. Whilst previous research has involved explicit representational processes, our results suggest that we can implicit access to a 'structural description of the body' and elaborate the anatomical and bio-mechanical plausibility.

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.

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.

On the relations between action planning, object identification, and motor representations of observed actions and objects.

Recent evidence suggests that viewing a static prime object (a hand grasp), can activate action representations that affect the subsequent identification of graspable target objects. The present study explored whether stronger effects on target object identification would occur when the prime object (a hand grasp) was made more action-rich and dynamic. Of additional interest was whether this type of action prime would affect the generation of motor activity normally elicited by the target object. Three experiments demonstrated that grasp observation improved the identification of grasp-congruent target objects relative to grasp-incongruent target objects. We argue from this data that identifying a graspable object includes the processing of its action-related attributes. In addition, grasp observation was shown to influence the motor activity elicited by the target object, demonstrating interplay between action-based and object-based motor coding.

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.

Visual object affordances: object orientation.

Five experiments systematically investigated whether orientation is a visual object property that affords action. The primary aim was to establish the existence of a pure physical affordance (PPA) of object orientation, independent of any semantic object-action associations or visually salient areas towards which visual attention might be biased. Taken together, the data from these experiments suggest that firstly PPAs of object orientation do exist, and secondly, the behavioural effects that reveal them are larger and more robust when the object appears to be graspable, and is oriented in depth (rather than just frontally) such that its leading edge appears to point outwards in space towards a particular hand of the viewer.

Local and global affordances and manual planning.

The present study aimed to demonstrate that motor planning processes are affected by ignored affordances of a main body of an object. Participants were asked to select the hand of response according to the property of the local component (a stalk) of the object (a fruit) while they were holding a precision or a power grip devices. The size of a main body of an object was observed to prime hand selection processes asymmetrically. Right-hand responses were facilitated when the stalk was a part of a precision grip object (e.g. a strawberry) or displayed alone. In contrast, left-hand responses were facilitated when the stalk was a part of a power grip object (e.g. an apple). This data supported our previously presented view that the different hemispheres have differential roles in the early planning of manual actions. The object information that is relevant to precision grip planning appears to be processed predominantly in the left-hemisphere whereas the information that is relevant to power grip planning appears to be processed predominantly in the right-hemisphere. In Experiment 3, the irrelevant fruit body had a slight effect on motor planning even though the stalk was spatially separated from the fruit body. The priming effect was entirely eliminated when, in addition to the spatial separation, the stalk was semantically disassociated from the fruit body (Experiment 4), and when the objects used in Experiment 1 were replaced by two dimensional abstract objects (Experiment 2). Experiments 2, 3 and 4 suggested that affordances of an irrelevant main body of an object influences motor planning processes only when the local target component of the object is analysed as a meaningful part of a graspable object.

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.