Action goal selection and motor planning can be dissociated by tool use
Introduction
Perception is enhanced at the goal of body movements during their preparation, relative to other locations. Such movement-related perceptual enhancement has been shown for saccadic eye movements (e.g., Deubel and Schneider, 1996, Doré-Mazars et al., 2004), manual reaching (Deubel, Schneider, & Paprotta, 1998) and grasping movements (Deubel and Schneider, 2004, Schiegg et al., 2003). Despite the fact that such an effect of action on perception has been observed in many studies, it remains unclear what cognitive processes underlie this effect. The intentional selection of a visual object as the goal of the next movement could lead to privileged perceptual processing at the spatial location of the goal; alternatively, planning a movement with specific motor coordinates could lead to enhanced perception at the end position of the planned movement. Usually, our actions are appropriate to the objects they aim for, and thus the position of the movement goal and that reached by the body movement coincide spatially. However, to examine which action process – goal selection or motor planning – underlies perceptual enhancement, these two positions must be dissociated experimentally.
The aim of the current study was to systematically dissociate the goal from the motor endpoint of a manual pointing movement. We did this by asking participants to point to visual targets with the tip of different hand-held tools (see illustrations in Fig. 1a). The position that must be reached by the finger while moving the tool (i.e., the motor endpoint) was different from the movement goal (the visual target the participants were to point to with the tool tip), the difference between the two depending on the shape of the tool. Participants prepared to place the tip of the tool on the visual target cued by a central arrow. During movement preparation, visual discrimination stimuli were presented at different positions, corresponding to the movement goal (tool endpoint), the motor endpoint (fingertip endpoint) or one of several other locations.
If perceptual enhancement at aimed-for locations depends on goal selection processes, then perception should be enhanced only when the discrimination target appears at the tool endpoint location (i.e., at the cued movement target location). If, on the contrary, motor planning processes lead to perceptual enhancement, then performance should be better when the discrimination target appeared at the location of the finger motor endpoint. A third possibility is that both goal selection and motor planning influence perception. In that case, we would expect perceptual performance to be better at both the cued location and at the motor endpoint relative to other locations.
We ran five experiments. Experiments 1–4 tested discrimination performance at different locations on and around the finger and tool with tools of various shapes. Our aim was to determine at which locations perceptual enhancement occurred. Experiment 5 examined performance in a task which required two targets to be compared. The goal was to determine whether perceptual enhancement occurred in parallel or serially between cued and motor endpoint locations.
Section snippets
Participants
Nine right-handed participants (aged 20–42 years, mean 30 years; five women) with normal visual acuity and no known neurological disorders took part in exchange for payment or course credit. One of the authors (T.C.) took part. All others were naïve regarding the object of the experiment. All gave their informed consent prior to starting the experiment, which was carried out according to the ethical standards of the Declaration of Helsinki (2008).
Stimuli and instruments
Visual stimuli were 1° by 1° black asterisks
Methods
Six participants (aged 20–40, mean 27; two women; one author) who also participated in Experiment 1 took part in exchange for payment. All gave their informed consent prior to starting the experiment, which was carried out according to the Declaration of Helsinki (2008).
Stimuli and procedures were identical to Experiment 1, except that eight placeholders indicated the locations at which the DT might occur. The four new placeholders were located midway between the original four locations.
Methods
Six volunteers (aged 21–28, mean 24; two women) received payment in exchange for their participation in Experiment 3. All had normal visual acuity and no known neurological disorders. None had participated in the previous experiments and all were naïve regarding the object of the experiment, except one author (T.C.). All gave their informed consent prior to starting the experiment, which was carried out according to the Declaration of Helsinki (2008).
Experiment 3 differed from Experiment 1 in
Methods
Eight volunteers (aged 21–28, mean 24; two women) took part in Experiment 4 in exchange for payment. All had normal visual acuity and no known neurological disorders. Four had participated in Experiment 3, including one author (T.C.). All gave their informed consent prior to starting the experiment, which was carried out according to the Declaration of Helsinki (2008).
The tool was mirror-reversed with respect to Experiment 1: the tip extended to the right of the little finger (Fig. 1a, bottom),
Methods
Eight volunteers (aged 21–28, mean 24; three women) received payment in exchange for their participation. All had normal visual acuity and no known neurological disorders. Five had participated in Experiment 4, including one author (T.C.). All gave their informed consent prior to starting the experiment, which was carried out according to the Declaration of Helsinki (2008).
The stimuli and tool were identical to Experiment 1. However, participants performed a matching task based on that
General discussion
Our results suggest that both goal selection and motor planning processes contribute to orienting visuo-spatial attention throughout the visual field during the preparation of a manual pointing movement. Perception was enhanced for the movement endpoints of those two objects that are most relevant during tool use – the fingertip and the active part of the tool. In contrast, perception was not enhanced at other spatial locations. Perception was high at the spatial location which was to be
Acknowledgments
T.C. is supported by an Alexander von Humboldt Foundation Research Fellowship. The authors thank Sybille Röper and Jonathan Schubert for help with data acquisition and Rainer Schäfer for technical assistance.
References (31)
- et al.
Deployment of visual attention before sequences of goal-directed hand movements
Vision Research
(2006) Task combination and selective intake of information
Acta Psychologica
(1982)- et al.
Saccade target selection and object recognition: Evidence for a common attentional mechanism
Vision Research
(1996) - et al.
Parieto-frontal interactions, personal space, and defensive behavior
Neuropsychologia
(2006) - et al.
Extending or projecting peripersonal space with tools? Multisensory interactions highlight only the distal and proximal ends of tools
Neuroscience Letters
(2004) - et al.
Tool-use: Capturing multisensory spatial attention or extending multisensory peripersonal space?
Cortex
(2007) - et al.
Tool-use changes multimodal spatial interactions between vision and touch in normal humans
Cognition
(2002) - et al.
The cortical motor system
Neuron
(2001) - et al.
Multisensory contributions to the 3-D representation of visuotactile peripersonal space in humans: Evidence from the crossmodal congruency task
Journal of Physiology Paris
(2004) - et al.
Properties of attentional selection during the preparation of sequential saccades
Experimental Brain Research
(2008)