Movement observation affects movement execution in a simple response task
Introduction
The present study can be placed in two different theoretical and experimental contexts: research on stimulus–response compatibility (SRC) and on action imitation. Usually these two fields are considered largely isolated from each other. This paper, however, argues that there is a close relationship between them. For this purpose, a theoretical framework is introduced that integrates both perspectives. Research on imitation may thus benefit from theoretical and experimental accounts of the SRC field about the question of how perception and action interact, while SRC research may benefit from the investigation of more complex stimulus–response (S–R) relations than has typically been done in this field.
The study of imitation phenomena has a long history, not only in psychology but in ethology and anthropology as well. Although imitation is well-documented in different fields of research and species (e.g., Fiorito and Scotto, 1992, Williams and Nottebohm, 1985), it is fair to say that the mechanisms underlying imitation are still poorly understood. From an action perspective, the most fundamental question of imitation may be described as “How can a motor act be constructed from a perceived act? Since, if we observe somebody executing a movement, we do not perceive the muscle activation underlying the movement. So how can we know which muscle movements will generate a movement that looks like the one we have observed?” (Prinz, 1987). Several attempts to solve this issue have been made. Some authors tried to reduce the problem to an instrumental learning Gewirtz, 1969, Gewirtz and Stingle, 1968 or an associative learning mechanism (Pawlby, 1977). One of the most elaborated and influential theories on imitation was proposed by Piaget (1962). His developmental theory of imitation was built around the concept of circular reactions. Infants explore the relation between motor act and the sensory effect of that action by performing specific actions repetitively. During this repetition process a link is established between the perceived act and the motor execution. When a child observes an adult while executing a movement similar to the visual component of their own visual–motor circular reactions, the respective motor component is triggered in the infant. While the observer interprets the infant’s behavior as imitation, the child is just repeating a circular reaction where the impetus to repeat the circle comes from the perception of the visual component of the ensemble (Meltzoff & Moore, 1983).
This interpretation cannot explain all imitation phenomena, as was pointed out by Meltzoff and Moore (1977) who detected very early imitation of facial gestures in neonates. Neonates cannot build a visual representation of their own facial gestures and, hence, the perceived gesture of a model cannot trigger the motor act by replacing this representation. Still the described mechanism underlying circular reactions might provide a first hint to a possible solution of the action problem in imitation. Namely, when we observe a movement we see the expected outcome of a potential self-executed movement. This view of imitation is very close to an early theory of motor control, the ideomotor theory, which will be described in the next paragraph.
An interesting suggestion concerning the relationship of perceived and executed action was given by James more than hundred years ago with the description of what he called ideomotor action (James, 1890). James formulated this idea as follows: “Every representation of a movement awakens in some degree the actual movement which is its object” (James, 1890, p. 1134). Greenwald (1970a) elaborated on this idea in his theory of ideomotor action. He stated (Greenwald, 1970b) that (a) voluntary responses are represented centrally in the form of images of the sensory feedback they produce, and (b) such images play a controlling role in the performance of their corresponding actions. From this perspective it becomes clear how action observation can be used to guide action execution. The visual response image is one of the major parts of sensory action feedback. Due to a similarity relation, observing an action activates the response image of the corresponding response, which in turn controls the observer’s performance. This ideomotor mechanism can be applied to account for imitation phenomena, but it is not restricted to imitation. Greenwald (1972) extended this idea to compatibility phenomena, forming the concept of ideomotor compatibility, which denotes “the extent to which a stimulus corresponds to sensory feedback from its required response” (p. 52). Ideomotor theory implies that stimuli with high ideomotor compatibility lead to an activation of the corresponding response via the activation of the response image. From this perspective, phenomena of SRC and imitation are closely related. Hence, research on imitative behavior and on SRC can be combined under the theoretical framework of ideomotor theory.
What assumptions can be drawn from ideomotor theory with regard to the concept of (ideomotor) compatibility? One of the central ideas of the theory is that perceiving the sensory feedback of an action leads to an activation of the response image. This image plays a controlling role in the performance of the action, assuming that no specific S–R translation is involved. In contrast, most models of SRC presuppose that S–R compatibility effects arise at the S–R translation stage (e.g., Hasbroucq & Guiard, 1991). Hence, if a response can be selected before the imperative signal appears, the selection process cannot be affected by the stimulus (however, see Hommel, 1997, for an alternative view).
In accordance with theories assuming that SRC operates on S–R translation stage, simple response tasks (SRT) yielded no or only very small S–R effects (e.g., Callan et al., 1974, Marzi et al., 1991, Bashore, 1981, Hasbroucq et al., 1988). In SRT paradigm, participants always have to execute the same response, that is, a task in which participants react with a predetermined left- or right-hand response, while random left and right stimuli are presented. The absence of robust effects in SRT paradigms seems to support the view that SRC is restricted to choice response tasks. However, in most studies the S–R arrangement was not highly ideomotor compatible. This might be the reason why the effects were typically found to be small. According to the ideomotor principle, SRC effects are expected even in an SRT, where the same response is required independent of the stimulus. The ideomotor theory assumes that even in an SRT, a response image is generated. Observing an action, presumably, evokes a response image as well. Therefore, compatibility between the act seen and the act to be performed should facilitate response execution by activating the actual response image, whereas an incompatible action should interfere with response execution.
The general aim of the present study was to investigate the implications of the ideomotor theory for views on imitation and on SRC. Particularly, the study addressed the question of whether S–R arrangements with high ideomotor compatibility lead to compatibility effects in a task with minimal response selection requirements. In addition, we wanted to investigate the ideomotor interpretation of imitation, which suggests that observing a movement activates the equivalent movement.
In order to do so, participants were required to execute a pre-instructed finger movement in response to the onset of a visually presented compatible or incompatible finger movement. When the observed movement is compatible to the pre-instructed movement this can be interpreted as a ‘quasi-imitative’ situation, that is, the subject performs a similar action as the action shown on the screen. Perceiving a compatible movement should activate the pre-instructed movement, which should result in faster reaction times. In addition, if the observed movement is incompatible with the instructed movement, the incompatible response is activated and thus needs to be inhibited, resulting in slower reaction times.
Section snippets
Experiment 1
The first experiment was a simple response task, in which participants executed the same finger movement within one block while reacting to the onset of a finger movement on a screen. The observed movement, which served as a go-signal for the predefined response, was compatible or incompatible with the to-be-executed response. In one block, the required movement was always to lift the index finger from a neutral starting position, that is the finger was held a few centimeters above the table.
Experiment 2
In Experiment 2 participants again were instructed to execute upward and downward finger movements in response to the same finger movements. However, in addition to this replication of Experiment 1, moving squares were presented. If the large compatibility effect in Experiment 1 was due to the amount of ideomotor compatibility, the compatibility effect should be much smaller when the go-signal is provided by an object movement. If, however, the large compatibility effect of Experiment 1 only
Experiment 3
To distinguish `movement direction' from the `type of movement', Experiment 3 was sub-divided: One part was a pure replication of Experiment 1. In the other part, everything was identical except that the original stimuli were flipped upside down. Thus, the former tapping movement now led to an upward movement, and vice versa (Fig. 5). This design allows for an opposite prediction regarding the compatibility effect for movement direction (up vs. down) and type of movement (tapping vs. lifting).
General discussion
The primary aim of the present study was to investigate whether a stimulus–response arrangement with high ideomotor compatibility leads to a compatibility effect in a task with minimal response-selection requirements as was predicted by the ideomotor theory. The result of Experiment 1 clearly supports this prediction showing a pronounced compatibility effect. In Experiment 2 we tested whether the effect observed in Experiment 1 was primarily related to some kind of general dynamic spatial
Acknowledgements
We thank Dirk Kerzel and Bas Neggers for technical support and comments on an earlier version of this paper, Heidi John for improving the English, Susanne Schorb for data collection and Frank Miedreich for assistance in programming.
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