Automatic imitation of intransitive actions

Previous research has indicated a potential discontinuity between monkey and human ventral premotor-parietal mirror systems, namely that monkey mirror systems process only transitive (object-directed) actions, whereas human mirror systems may also process intransitive (non-object-directed) actions. The present study investigated this discontinuity by seeking evidence of automatic imitation of intransitive actions--hand opening and closing--in humans using a simple reaction time (RT), stimulus-response compatibility paradigm. Left-right and up-down spatial compatibility were controlled by ensuring that stimuli were presented and responses executed in orthogonal planes, and automatic imitation was isolated from simple and complex orthogonal spatial compatibility by varying the anatomical identity of the stimulus hand and response hemispace, respectively. In all conditions, action compatible responding was faster than action incompatible responding, and no effects of spatial compatibility were observed. This experiment therefore provides evidence of automatic imitation of intransitive actions, and support for the hypothesis that human and monkey mirror systems differ with respect to the processing of intransitive actions.     

Imitative response tendencies following observation of intransitive actions

Clear and unequivocal evidence shows that observation of object affordances or transitive actions facilitates the activation of a compatible response. By contrast, the evidence showing response facilitation following observation of intransitive actions is less conclusive because automatic imitation and spatial compatibility have been confounded. Three experiments tested whether observation of a finger movement (i.e., an intransitive action) in a choice reaction-time task facilitates the corresponding finger movement response because of imitation, a common spatial code, or some combination of both factors. The priming effects of a spatial and an imitative stimulus were tested in combination (Experiment 1), in opposition (Experiment 2), and independently (Experiment 3). Contrary to previous findings, the evidence revealed significant contributions from both automatic imitation and spatial compatibility, but the priming effects from an automatic tendency to imitate declined significantly across a block of trials whereas the effects of spatial compatibility remained constant or increased slightly. These differential effects suggest that priming associated with automatic imitation is mediated by a different regime than priming associated with spatial compatibility.     

Are Automatic Imitation and Spatial Compatibility Mediated by Different Processes?

Automatic imitation or “imitative compatibility” is thought to be mediated by the mirror neuron system and to be a laboratory model of the motor mimicry that occurs spontaneously in naturalistic social interaction. Imitative compatibility and spatial compatibility effects are known to depend on different stimulus dimensions—body movement topography and relative spatial position. However, it is not yet clear whether these two types of stimulus–response compatibility effect are mediated by the same or different cognitive processes. We present an interactive activation model of imitative and spatial compatibility, based on a dual‐route architecture, which substantiates the view they are mediated by processes of the same kind. The model, which is in many ways a standard application of the interactive activation approach, simulates all key results of a recent study by Catmur and Heyes (2011) . Specifically, it captures the difference in the relative size of imitative and spatial compatibility effects; the lack of interaction when the imperative and irrelevant stimuli are presented simultaneously; the relative speed of responses in a quintile analysis when the imperative and irrelevant stimuli are presented simultaneously; and the different time courses of the compatibility effects when the imperative and irrelevant stimuli are presented asynchronously.     

Automatic imitation of biomechanically possible and impossible actions: effects of priming movements versus goals

Recent behavioral, neuroimaging, and neurophysiological research suggests a common representational code mediating the observation and execution of actions; yet, the nature of this representational code is not well understood. The authors address this question by investigating (a) whether this observation-execution matching system (or mirror system) codes both the constituent movements of an action as well as its goal and (b) how such sensitivity is influenced by top-down effects of instructions. The authors tested the automatic imitation of observed finger actions while manipulating whether the movements were biomechanically possible or impossible, but holding the goal constant. When no mention was made of this difference (Experiment 1), comparable automatic imitation was elicited from possible and impossible actions, suggesting that the actions had been coded at the level of the goal. When attention was drawn to this difference (Experiment 2), however, only possible movements elicited automatic imitation. This sensitivity was specific to imitation, not affecting spatial stimulus-response compatibility (Experiment 3). These results suggest that automatic imitation is modulated by top-down influences, coding actions in terms of both movements and goals depending on the focus of attention.     

Automatic imitation

"Automatic imitation" is a type of stimulus-response compatibility effect in which the topographical features of task-irrelevant action stimuli facilitate similar, and interfere with dissimilar, responses. This article reviews behavioral, neurophysiological, and neuroimaging research on automatic imitation, asking in what sense it is "automatic" and whether it is "imitation." This body of research reveals that automatic imitation is a covert form of imitation, distinct from spatial compatibility. It also indicates that, although automatic imitation is subject to input modulation by attentional processes, and output modulation by inhibitory processes, it is mediated by learned, long-term sensorimotor associations that cannot be altered directly by intentional processes. Automatic imitation provides an important tool for the investigation of the mirror neuron system, motor mimicry, and complex forms of imitation. It is a new behavioral phenomenon, comparable with the Stroop and Simon effects, providing strong evidence that even healthy adult humans are prone, in an unwilled and unreasoned way, to copy the actions of others.     

Is automatic imitation a specialized form of stimulus–response compatibility? Dissociating imitative and spatial compatibilities

In recent years research on automatic imitation has received considerable attention because it represents an experimental platform for investigating a number of interrelated theories suggesting that the perception of action automatically activates corresponding motor programs. A key debate within this research centers on whether automatic imitation is any different than other long-term S-R associations, such as spatial stimulus-response compatibility. One approach to resolving this issue is to examine whether automatic imitation shows similar response characteristics as other classes of stimulus-response compatibility. This hypothesis was tested by comparing imitative and spatial compatibility effects with a two alternative forced-choice stimulus-response compatibility paradigm. The stimulus on each trial was a left or right hand with either the index or middle finger tapping down. Speeded responses were performed with the index or middle finger of the right hand in response to the identity or the left-right spatial position of the stimulus finger. Two different tasks were administered: one that involved responding to the stimulus (S-R) and one that involved responding to the opposite stimulus (OS-R; i.e., the one not presented on that trial). Based on previous research and a connectionist model, we predicted standard compatibility effects for both spatial and imitative compatibility in the S-R task, and a reverse compatibility effect for spatial compatibility, but not for imitative compatibility, in the OS-R task. The results from the mean response times, mean percentage of errors, and response time distributions all converged to support these predictions. A second noteworthy result was that the recoding of the finger identity in the OS-R task required significantly more time than the recoding of the left-right spatial position, but the encoding time for the two stimuli in the S-R task was equivalent. In sum, this evidence suggests that the processing of spatial and imitative compatibility is dissociable with regard to two different processes in dual processing models of stimulus-response compatibility.     

Updating representations of learned scenes

Two experiments were designed to compare scene recognition reaction time (RT) and accuracy patterns following observer versus scene movement. In Experiment 1, participants memorized a scene from a single perspective. Then, either the scene was rotated or the participants moved (0°–360° in 36° increments) around the scene, and participants judged whether the objects’ positions had changed. Regardless of whether the scene was rotated or the observer moved, RT increased with greater angular distance between judged and encoded views. In Experiment 2, we varied the delay (0, 6, or 12 s) between scene encoding and locomotion. Regardless of the delay, however, accuracy decreased and RT increased with angular distance. Thus, our data show that observer movement does not necessarily update representations of spatial layouts and raise questions about the effects of duration limitations and encoding points of view on the automatic spatial updating of representations of scenes.     

A role for set in the control of automatic spatial response activation

Spatial stimulus-response (S-R) compatibility effects are widely assumed to reflect the automatic activation of a spatial response by the spatial attributes of a stimulus. The experiments reported here investigate the role of the participant's set in enabling or interacting with this putatively automatic spatial response activation. Participants performed a color discrimination task (Experiment 1) or a localization task (Experiment 2). In each experiment, two different S-R mappings were used and a task-cue indicated the appropriate mapping on each trial. S-R compatibility and the time between the task-cue and target were manipulated, and compatibility effects were assessed as a function of (a) the time between the task-cue and the stimulus, and (b) whether the S-R mapping repeated or switched on consecutive trials. Critically, whether response mappings repeated or switched on consecutive trials determined the relation between compatibility effects and the time between task-cue and stimulus. These results are discussed in terms of an interaction between automatic spatial response activation and the participant's set.     

Movement observation affects movement execution in a simple response task

The present study was designed to examine the hypothesis that stimulus-response arrangements with high ideomotor compatibility lead to substantial compatibility effects even in simple response tasks. In Experiment 1, participants executed pre-instructed finger movements in response to compatible and incompatible finger movements. A pronounced reaction time advantage was found for compatible as compared to incompatible trials. Experiment 2 revealed a much smaller compatibility effect for less ideomotor-compatible object movements compared to finger movements. Experiment 3 presented normal stimuli (hand upright) and flipped stimuli (hand upside-down). Two components were found to contribute to the compatibility effect, a dynamic spatial compatibility component (related to movement directions) and an ideomotor component (related to movement types). The implications of these results for theories about stimulus-response compatibility (SRC) as well as for theories about imitation are discussed.     

Attentional focussing and spatial stimulus-response compatibility

Summary The relative functional significance of attention shifts and attentional zooming for the coding of stimulus position in spatial compatibility tasks is demonstrated by proposing and testing experimentally a tentative explanation of the absence of a Simon effect in Experiment 3 of Umiltà and Liotti (1987). It is assumed that the neutral point of the spatial frame of reference for coding spatial position is at the position where attention is focussed immediately before exposition of the stimulus pattern. If a stimulus pattern is exposed to the right or the left of this position a spatial compatibility effect can be observed when the stimulus-response pairing is incompatible. Generalizing from this, one can say that a spatial compatibility effect will be observed if the last step in attentional focussing of the stimulus attribute specifying the response is a horizontal or a vertical attention shift. If the last step in focussing is attentional zooming (change in the representational level attended to), the stimulus pattern is localized at the horizontal and the vertical positions where the last attention shift had positioned the focus. In this case the spatial code is neutral on these dimensions and so no spatial compatibility effect should result. To test this model we conducted two experiments. Experiment 1 replicated the finding of Umiltà and Liotti that there is no Simon effect in the condition with no delay between a positional cue (two small boxes on the left or right of a fixation cross) and the imperative stimulus, whereas in the condition with a delay of 500 ms a Simon effect was observed. In a comparison condition with a single, rather large cue instead of two small boxes (forcing attention to zoom in), no Simon effect was observed under either delay condition. Experiment 2 used a spatial compatibility task proper with the same experimental conditions as Experiment 1. But in contrast to those of Experiment 1, the results show strong compatibility effects in all cue and delay conditions. The absence of a Simon effect in some experimental conditions in Experiment 1 and the presence of a spatial compatibility effect proper in all conditions in Experiment 2 are consistently accounted for with the proposed attentional explanation of spatial coding and spatial compatibility effects.     

Visual field asymmetries and allocation of attention in visual scenes

Single items such as objects, letters or words are often presented in the right or left visual field to examine hemispheric differences in cognitive processing. However, in everyday life, such items appear within a visual context or scene that affects how they are represented and selected for attention. Here we examine processing asymmetries for a visual target within a frame of other elements (scene). We are especially interested in whether the allocation of visual attention affects the asymmetries, and in whether attention-related asymmetries occur in scenes oriented out of alignment with the viewer. In Experiment 1, visual field asymmetries were affected by the validity of a spatial precue in an upright frame. In Experiment 2, the same pattern of asymmetries occurred within frames rotated 90 degrees on the screen. In Experiment 3, additional sources of the spatial asymmetries were explored. We conclude that several left/right processing asymmetries, including some associated with the deployment of spatial attention, can be organized within scenes, in the absence of differential direct access to the two hemispheres.     

S-R Compatibility Effects Without Response Uncertainty

Five experiments investigated whether cognitively based spatial S-R correspondence effects or "compatibility" effects can occur in simple reaction time (SRT) tasks and if so, which factors might be responsible for their occurrence and size. In Experiment 1, responses were cued before each trial, but made only after presentation of a Go signal. There were considerably faster responses with spatial correspondence of Go signal and response, demonstrating that response certainty does not prevent a compatibility effect. Experiment 2, a SRT task with "extra" trials requiring responses with the same or the opposite hand, indicated a major determinant of this effect to be the keeping of two task-relevant responses in a state of readiness. Experiment 3 provided preliminary evidence for 'inertia' effects-that is, for stronger correspondence effects with frequent than with infrequent alternations between left-hand and right-hand blocks. Experiment 4 showed that correspondence effects can be obtained by using a within-hand response repertoire. Experiment 5, a replication of Experiment 3 with within-hand responses, found further evidence for inertia effects. For all experiments, reaction time distribution analyses were carried out to gain insight into the temporal dynamics of correspondence effects. Altogether the results strongly suggest that most if not all correspondence effects had a cognitive rather than an anatomical origin. This raises some doubts about conclusions from prior attempts to measure interhemispheric transmission costs by means of SRT tasks.     

Set- and Element-Level Stimulus-Response Compatibility Effects for Different Manual Response Sets

In a previous study of two-choice reactions, pairings of spatial stimuli with bimanual presses made on a keyboard and verbal stimuli with unimanual aimed movements made on a display screen showed higher set-level compatibility than the opposite pairings; element-level compatibility (i.e., mapping) effects were also larger for the conditions with high set-level compatibility than for those whose set-level compatibility was low. In the 4 experiments described here, the relevant factors were isolated, allowing the determinants of those compatibility differences to be evaluated in more detail. Forty-eight students participated in Experiment 1, and 24 each in Experiments 2, 3, and 4. The primary determinant of the set-level compatibility variation was whether the response alternatives involved 1 or 2 effectors, but the differences in element-level compatibility effects were determined primarily by the distinction between responding on the screen as opposed to on the keyboard. Implications for models of stimulus-response compatibility are examined.     

Spatial S-R compatibility effects in an intentional imitation task

The active intermodal mapping hypothesis suggests that intentional imitation is mediated by a highly efficient, special-purpose mechanism of actor-centered movement encoding. In the present study, using methods from stimulus-response (S-R) compatibility research, we found no evidence to support this hypothesis. In two experiments, the performance of adult participants instructed to imitate actorcentered spatial properties of head, arm, and leg movements was affected by task-irrelevant, egocentric spatial cues. In Experiment 1, participants imitated using the same side of their bodies as did the model, and performance was less accurate when egocentric stimulus location was response incompatible than when it was response compatible. This effect was reversed in Experiment 2 when participants imitated using the opposite side of their bodies. These findings, in line with general process theories of imitation, imply that intentional imitation is mediated by the same processes that mediate responding to inanimate stimuli on the basis of arbitrary S-R mappings.     

Disentangling boundary extension and normalization of view memory for scenes

Boundary extension (BE) is a memory error for close-up views of scenes in which participants tend to remember a picture of a scene as depicting a more wide-angle view than what was actually displayed. However, some experiments have yielded data that indicate a normalized memory of the views depicted in a set of scenes, suggesting that memory for the previously studied scenes has become drawn toward the average view in the image set. In previous studies, normalization is only found when the retention interval is very long or when the stimuli no longer appear to represent a spatial expanse. In Experiment 1, we examine whether normalization can influence results for scenes depicting a partial view of space and when the memory test occurs immediately following the study block by manipulating the degree of difference between studied close-up and wide-angle scenes. In Experiment 2, normalization is induced in a set of scenes by creating conditions expected to lead to memory interference, suggesting that this may be the cause of view normalization. Based on the multi-source model of BE, these scenes should be extended during perception (Intraub, H. (2010). Rethinking scene perception: A multisource model. Psychology of Learning and Motivation, 52, 231–265). In Experiment 3, we show that BE is indeed observable if the same scenes are tested differently, supporting the notion that BE is primarily a perceptual phenomenon while normalization is a memory effect.     

To point a finger: attentional and motor consequences of observing pointing movements

Recent studies showed that action observation activates neural circuits used in performing the same action and facilitates execution of a similar motor program. This system for direct mapping of observed actions onto observer’s own motor representation is considered critical for human imitation capabilities. The present study shows that observing a pointing action activates a representation of that action in anatomical space, irrespectively of whether the action is shown in allocentric or egocentric perspective. This finding is at odds with the studies on imitation which showed that humans tend to imitate in a spatially compatible (specular) way, as if looking in a mirror. Our results suggest that shared representations for actions are organized in the same spatial coordinates; however, a transformation of this representation might be required for imitation tasks in order to accommodate the goals of imitative action.     

Correction: Two-action task,testing imitative social learning in kea (Nestor notabilis)

Social learning is an adaptive way of dealing with the complexity of life as it reduces the risk of trial-and-error learning. Depending on the type of information acquired, and associations formed, several mechanisms within the larger taxonomy of social learning can be distinguished. Imitation is one such process within this larger taxonomy, it is considered cognitively demanding and is associated with high-fidelity response matching. The present study reproduced a 2002 study conducted by Heyes and Saggerson, which successfully illustrated motor imitation in budgerigars (Melopsittacus undulatus). In our study, eighteen kea (Nestor notabilis) that observed a trained demonstrator remove a stopper from a test box (1) took less time from hopping on the box to feeding (response duration) in session one and (2) were faster in making a vertical removal response on the stopper once they hopped on the box (removal latency) in session one than non-observing control group individuals. In contrast to the budgerigars (Heyes and Saggerson, Ani Behav. 64:851–859, 2002) the present study could not find evidence of motor imitation in kea. The results do illustrate, however, that there were strong social effects on exploration rates indicating motivational and attentional shifts. Furthermore, the results may suggest a propensity toward emulation in contrast to motor imitation or alternatively selectivity in the application of imitation.

     

The Lateral Coding of Rotations

A number of experimental studies have consistently shown the locus of spatial S-R compatibility effects to be the selection of the response within an abstract memory code. The purpose of the present study was to test, in the particular case of wheel rotations, the general proposition that any response that a subject internally codes in terms of left and right may be interfered with by the lateral location of the stimuli in a Simon paradigm. Experiment 1 showed that the auditory Simon effect occurred in a task where the subjects had to rotate a steering wheel bimanually either clockwise or counterclockwise according to sound pitch, despite the fact that responses of this kind are undefined with respect to laterality. Experiment 2 confirmed this result in a unimanual rotation condition and suggested that the ear-rotation compatibility effect may be added to the effect of a biomechanical factor, pronation versus supination, supporting the idea of an abstract motor code. In Experiment 3, subjects rotated the steering wheel with their hands on the lowest part of the wheel. When the response movement made the spot of a C.R.T. move laterally in accordance with the performed rotation, the subjects coded their response directly in terms of its effect on the visual display. For subjects not receiving visual feedback, no compatibility effect occurred. However, the individual data were compatible with the notion that some subjects in this group coded their responses in terms of wheel rotations, and others in terms of hand movements.     

Reducing and restoring stimulus-response compatibility effects by decreasing the discriminability of location words

In two experiments, we compared level of activation and temporal overlap accounts of compatibility effects in the Simon task by reducing the discriminability of spatial and non-spatial features of a target location word. Participants made keypress responses to the non-spatial or spatial feature of centrally presented location words. The discriminability of the spatial feature of the word (Experiment 1), or of both the spatial and non-spatial feature (Experiment 2), was manipulated. When the spatial feature of the word was task-irrelevant, lowering the discriminability of this feature reduced the compatibility effect. The compatibility effect was restored when the discriminability of both the task-relevant and task-irrelevant features were reduced together. Results provide further evidence for the temporal overlap account of compatibility effects. Furthermore, compatibility effects when the spatial information was task-relevant and those when the spatial information was task-irrelevant were moderately correlated with each other, suggesting a common underlying mechanism in both versions.     

The lateral coding of rotations: a study of the simon effect with wheel-rotation responses

A number of experimental studies have consistently shown the locus of spatial S-R compatibility effects to be the selection of the response within an abstract memory code. The purpose of the present study was to test, in the particular case of wheel rotations, the general proposition that any response that a subject internally codes in terms of left and right may be interfered with by the lateral location of the stimuli in a Simon paradigm. Experiment 1 showed that the auditory Simon effect occurred in a task where the subjects had to rotate a steering wheel bimanually either clockwise or counterclockwise according to sound pitch, despite the fact that responses of this kind are undefined with respect to laterality. Experiment 2 confirmed this result in a unimanual rotation condition and suggested that the ear-rotation compatibility effect may be added to the effect of a biomechanical factor, pronation versus supination, supporting the idea of an abstraction motor code. In Experiment 3, subjects rotated the steering wheel with their hands on the lowest part of the wheel. When the response movement made the spot of a C.R.T. move laterally in accordance with the performed rotation, the subjects coded their response directly in terms of its effect on the visual display. For subjects not receiving visual feedback, no compatibility effect occurred. however, the individual data were compatible with the notion that some subjects in this group coded their responses in terms of wheel rotations, and others in terms of hand movements.