Action observation produces motor resonance in Parkinson's disease

Observation of movement activates the observer's own motor system, influencing the performance of actions and facilitating social interaction. This motor resonance is demonstrated behaviourally through visuomotor priming, whereby response latencies are influenced by the compatibility between an intended action and an observed (task‐irrelevant) action. The impact of movement disorders such as Parkinson's disease (PD) on motor resonance is unclear, as previous studies of visuomotor priming have not separated imitative compatibility (specific to human movement) from general stimulus‐response compatibility effects. We examined visuomotor priming in 23 participants with mild‐to‐moderate PD and 24 healthy older adults, using a task that pitted imitative compatibility against general stimulus‐response compatibility. Participants made a key press after observing a task‐irrelevant moving human finger or rectangle that was either compatible or incompatible with their response. Imitative compatibility effects, rather than general stimulus‐response compatibility effects, were found specifically for the human finger. Moreover, imitative compatibility effects did not differ between groups, indicating intact motor resonance in the PD group. These findings constitute the first unambiguous demonstration of imitative priming in both PD and healthy ageing, and have implications for therapeutic techniques to facilitate action, as well as the understanding of social cognition in PD.     

The influence of dimensional overlap on location-related priming in the Simon task

Choice reaction times are shorter when stimulus and response locations are compatible than when they are incompatible as in the Simon effect. Recent studies revealed that Simon effects are strongly attenuated when there is temporal overlap with a different high-priority task, accompanied by a decrease of early location-related response priming as reflected in the lateralized readiness potential (LRP). The latter result was obtained in a study excluding overlap of stimulus location with any other dimension in the tasks. Independent evidence suggests that location-related priming might be present in conditions with dimensional overlap. Here we tested this prediction in a dual-task experiment supplemented with recording LRPs. The secondary task was either a standard Simon task where irrelevant stimulus location overlapped with dimensions of the primary task or a Stroop-like Simon task including additional overlap of irrelevant and relevant stimulus attributes. At high temporal overlap, there was no Simon effect nor was there stimulus-related response priming in either condition. Therefore stimulus-triggered response priming seems to be abolished in conditions of limited capacity even if the likelihood of an S–R compatibility effect is maximized.     

Seeing while moving: measuring the online influence of action on perception

The online influence of movement production on motion perception was investigated. Participants were asked to move one of their hands in a certain direction while monitoring an independent stimulus motion. The stimulus motion unpredictably deviated in a direction that was either compatible or incompatible with the concurrent movement. Participants' task was to make a speeded response as soon as they detected the deviation. A reversed compatibility effect was obtained: Reaction times were slower under compatible conditions—that is, when motion deviations and movements went in the same direction. This reversal of a commonly observed facilitatory effect can be attributed to the concurrent nature of the perception-action task and to the fact that what was produced was functionally unrelated to what was perceived. Moreover, by employing an online measure, it was possible to minimize the contribution of short-term memory processes, which has potentially confounded the interpretation of related effects.     

Seeing while moving: Measuring the online influence of action on perception

The online influence of movement production on motion perception was investigated. Participants were asked to move one of their hands in a certain direction while monitoring an independent stimulus motion. The stimulus motion unpredictably deviated in a direction that was either compatible or incompatible with the concurrent movement. Participants' task was to make a speeded response as soon as they detected the deviation. A reversed compatibility effect was obtained: Reaction times were slower under compatible conditions—that is, when motion deviations and movements went in the same direction. This reversal of a commonly observed facilitatory effect can be attributed to the concurrent nature of the perception–action task and to the fact that what was produced was functionally unrelated to what was perceived. Moreover, by employing an online measure, it was possible to minimize the contribution of short-term memory processes, which has potentially confounded the interpretation of related effects.     

Reexamining the word length effect in visual word recognition: New evidence from the English Lexicon Project

In the present study, we reexamined the effect of word length (number of letters in a word) on lexical decision. Using the English Lexicon Project, which is based on a large data set of over 40,481 words (Balota et al., 2002), we performed simultaneous multiple regression analyses on a selection of 33,006 English words (ranging from 3 to 13 letters in length). Our analyses revealed an unexpected pattern of results taking the form of a U-shaped curve. The effect of number of letters was facilitatory for words of 3–5 letters, null for words of 5–8 letters, and inhibitory for words of 8–13 letters. We also showed that printed frequency, number of syllables, and number of orthographic neighbors all made independent contributions. The length effects were replicated in a new analysis of a subset of 3,833 monomorphemic nouns (ranging from 3 to 10 letters), and also in another analysis based on 12,987 bisyllabic items (ranging from 3 to 9 letters). These effects were independent of printed frequency, number of syllables, and number of orthographic neighbors. Furthermore, we also observed robust linear inhibitory effects of number of syllables. Implications for models of visual word recognition are discussed.     

Delayed constructed-response identity matching improves the spelling performance of students with mental retardation

We assessed the effects of a computerized matching-to-sample procedure on the spelling performances of three students with mental retardation. Initially, the students could 1) match pictures and printed words to one another, and 2) match pictures and printed words to spoken words. However, they could not construct words to either pictures or spoken words (e.g., touch, in order, the letters s->h->o->e given the spoken-word sample Shoe). Word constructions then improved markedly after exposure to delayed constructed-response identity matching (e.g., touch the letters s->h->o->e given the printed-word sample shoe). One subject's oral and written spelling also improved. The results extend previous research by showing multiple positive effects of a computerized spelling intervention. These effects may have occurred in part because of the formation of stimulus classes among pictures, printed words, and spoken words.     

Interactions between stimulus-stimulus congruence and stimulus-response compatibility

According to a central claim of Kornblum's dimensional-overlap model, response-related processes do not start before stimulus-related processes have been completed, which implies an additive relationship between effects of stimulus-stimulus congruence and stimulus-response compatibility. Three experiments were conducted to test this prediction. In Exp. 1, additive effects of color-word congruence (Stroop effect) and irrelevant spatial S-R compatibility (Simon effect) were in fact obtained. However, interactions between congruence and compatibility were observed in Exp. 2, where flanker-target congruence was varied, and in Exp. 3, where inter-level congruence of multi-level letters was manipulated. It is argued that these findings are inconsistent with the seriality assumption of the dimensional-overlap model, but that they support models claiming a temporal overlap of stimulus and response processing instead.     

Influence of stimulus type on effects of flanker,flanker position,and trial sequence in a saccadic eye movement task

Using the flanker paradigm in a task requiring eye movement responses, we examined how stimulus type (arrows vs. letters) modulated effects of flanker and flanker position. Further, we examined trial sequence effects and the impact of stimulus type on these effects. Participants responded to a central target with a left- or rightward saccade. We reasoned that arrows, being overlearned symbols of direction, are processed with less effort and are therefore linked more easily to a direction and a required response than are letters. The main findings demonstrate that (a) flanker effects were stronger for arrows than for letters, (b) flanker position more strongly modulated the flanker effect for letters than for arrows, and (c) trial sequence effects partly differed between the two stimulus types. We discuss these findings in the context of a more automatic and effortless processing of arrow relative to letter stimuli.     

Modulation of motor area activity during observation of unnatural body movements

We investigated the processes underlying stimulus-response compatibility by using a lateralized auditory stimulus in a simple and choice reaction time (RT) paradigm. Participants were asked to make either a left or right key lift in response to either a control (80 dB) or startling (124 dB) stimulus presented to either the left ear, right ear, or both ears. In the simple RT paradigm, we did not find a compatibility effect for either control or startle trials but did find a right-ear advantage which we attribute to anatomical asymmetry of auditory pathways. In the choice RT paradigm, we found compatibility effects for both startle and control trials as well a high incidence of error for contralateral stimulus-response mapping. We attribute these results to automatic activation of the ipsilateral response, which must then be inhibited prior to initiation of the correct response. The presence of compatibility effects for startle trials also suggest that similar pathways are being used to initiate movements in a choice RT situation, as opposed to involuntary triggering that is thought to occur in a simple RT situation.     

A computational model of action resonance and its modulation by emotional stimulation

Recent research has shown that stimulus–response compatibility (SRC) effects can be modulated by the emotional state of the participant and, more specifically, that the SRC effect is larger when aversive emotional stimulation precedes the seen movement [Rumiati, R. I. & Grecucci, A. (submitted for publication). On the emotional modulation of action]. In the present study, we propose that this effect arises from four assumptions: First, that the cortical representations subserving observation and execution of the same actions overlap and resonate; second, that graded persistence of activation due to observed movement facilitates subsequent movement execution; third, that movement representations that are similar but different compete for activation; and fourth, that aversive emotional states enhance the processing of events. By means of a set of simulations, we demonstrate that each of these assumptions plays a critical role in capturing the compatibility effect and its emotional modulation. We further employ the model to clarify the debate between synergistic and competitive views of cognition/emotion interactions, and demonstrate how emotionally-driven stimulus–response compatibility effects may be modulated by task demands, thus offering a possible resolution to the long-standing debate between synergistic and competitive interactions between emotion and cognition.     

Motor activation from visible speech: evidence from stimulus response compatibility

In speech perception, phonetic information can be acquired optically as well as acoustically. The motor theory of speech perception holds that motor control structures are involved in the processing of visible speech, whereas perceptual accounts do not make this assumption. Motor involvement in speech perception was examined by showing participants response-irrelevant movies of a mouth articulating /ba/ or /da/ and asking them to verbally respond with either the same or a different syllable. The letters "Ba" and "Da" appeared on the speaker's mouth to indicate which response was to be performed. A reliable interference effect was observed. In subsequent experiments, perceptual interference was ruled out by using response-unrelated imperative stimuli and by preexposing the relevant stimulus information. Further, it was demonstrated that simple directional features (opening and closing) do not account for the effect. Rather, the present study provides evidence for the view that visible speech is processed up to a late, response-related processing stage, as predicted by the motor theory of speech perception.     

An action sequence held in memory can interfere with response selection of a target stimulus,but does not interfere with response activation of noise stimuli

Withholding an action plan in memory for later execution can delay execution of another action if the actions share a similar (compatible) action feature (e.g., response hand). We investigated whether this phenomenon, termed compatibility interference (CI), occurs for responses associated with a target as well as responses associated with distractors in a visual selection task. Participants planned and withheld a sequence of keypress responses (with their right or left hand), according to the identity of a stimulus (A), and then immediately executed a keypress response (with their right or left hand) to a second stimulus (B), according to the identity of a target letter appearing alone or among distractor letters. Distractor letters were either response compatible or incompatible with the target and appeared either simultaneously with the target (Experiments 1A and 2) or 100 msec before the target (Experiment 1B). Also, stimulus-response mapping was either 1:1 (Experiment 1) or 2:1 (Experiment 2). Results showed that the response to the Stimulus B target was delayed when it required the same response hand as Stimulus A, as opposed to a different hand. Also, the target reaction time for Stimulus B was greater when the target was flanked by incompatible distractors than when it was flanked by compatible distractors. Moreover, the degree of CI was consistent across the compatible-, incompatible-, and no-distractor conditions, indicating that CI generalizes to responses associated with a target, but not to those associated with distractors. Thus, CI occurs at a response selection, not at a response activation stage. Implications for the code occupation account for CI (e.g., Stoet & Hommel, 1999, 2002) and an alternative account for CI are discussed.     

Differential dynamics of spatial and non-spatial stimulus-response compatibility effects: a dual task LRP study

Choice reaction times are shorter when stimulus and response features are compatible rather than incompatible. Recent studies revealed that spatial compatibility effects in Simon tasks are strongly attenuated when there is temporal overlap with a different high-priority task. In contrast, non-spatial variants of the Simon task appear to be unaffected by task overlap. The present study used the lateralized readiness potential (LRP) within a dual task design to elucidate the dynamics underlying these differential effects for a color and a spatial variant of the Simon task. In the color version there was no sign of early response priming by irrelevant stimulus features in the LRP. The color compatibility effect was independent of task overlap and reflected in the LRP onset latency. In contrast, in the spatial version, priming by irrelevant stimulus location showed up and was mirrored by early LRP activation. Response priming and the corresponding Simon effect, however, were present only in case of little temporal overlap with the primary task. The absence of spatial compatibility effects at strong temporal overlap suggests that response conflicts due to stimulus-related priming depend on the availability of processing resources.     

The effect of age of acquisition in visual word processing: further evidence for the semantic hypothesis

The authors investigated whether the meaning of visually presented words is activated faster for early-acquired words than for late-acquired words. They addressed the issue using the semantic Simon paradigm. In this paradigm, participants are instructed to decide whether a stimulus word is printed in uppercase or lowercase letters. However, they have to respond with a verbal label ("living" or "nonliving") that is either congruent with the meaning of the word (e.g., saying "living" to the stimulus DOG) or incongruent (e.g., saying "nonliving" to the stimulus dog). Results showed a significant congruency effect that was stronger for early-acquired words than for late-acquired words. The authors conclude that the age of acquisition is an important variable in the activation of the meaning of visually presented words.     

Effect of consonant/vowel letter organisation on the syllable counting task: evidence from English

Recent studies in alphabetic writing systems have investigated whether the status of letters as consonants or vowels influences the perception and processing of written words. Here, we examined to what extent the organisation of consonants and vowels within words affects performance in a syllable counting task in English. Participants were asked to judge the number of syllables in written words that were matched for the number of spoken syllables but comprised either 1 orthographic vowel cluster less than the number of syllables (hiatus words, e.g., triumph) or as many vowel clusters as syllables (e.g., pudding). In 3 experiments, we found that readers were slower and less accurate on hiatus than control words, even when phonological complexity (Experiment 1), number of reduced vowels (Experiment 2), and number of letters (Experiment 3) were taken into account. Interestingly, for words with or without the same number of vowel clusters and syllables, participants’ errors were more likely to underestimate the number of syllables than to overestimate it. Results are discussed in a cross-linguistic perspective.     

Approach and avoidance movements are unaffected by cognitive conflict: A comparison of the Simon effect and stimulus–response compatibility

Participants in this study reached from central fixation to a lateral position that either contained or was opposite to the stimulus. Cognitive conflict was induced when the stimulus and response directions did not correspond. In the Simon task, the response direction was cued by the color of the lateral stimulus, and corresponding and noncorresponding trials varied randomly in the same block of trials, resulting in high uncertainty and long reaction times (RTs). In the stimulus-response compatibility (SRC) task, participants reached toward or away from the stimulus in separate blocks of trials, resulting in low uncertainty and short RTs. In the SRC task, cognitive conflict in noncorresponding trials slowed down RTs but hardly affected reach trajectories. In the Simon task, both RTs and reach trajectories were strongly influenced by stimulus-response correspondence. Despite the overall longer RTs in the Simon task, reaches were less direct and deviated toward the stimulus in noncorresponding trials. Thus, cognitive conflict was resolved before movement initiation in the SRC task, whereas it leaked into movement execution in the Simon task. Current theories of the Simon effect, such as the gating of response activation or response code decay, are inconsistent with our results. We propose that the SRC task was decomposed as approaching and avoiding the stimulus, which is sustained by stereotyped visuomotor routines. With complex stimulus-response relationships (Simon task), responses had to be coded as leftward and rightward, with more uncertainty about how to execute the action. This uncertainty permitted cognitive conflict to leak into the movement execution.     

Stimulus-response compatibility effects in go-no-go tasks: a dimensional overlap account

According to the automatic response activation hypothesis of the dimensional overlap (DO) model (Kornblum, Stevens, Whipple, & Requin, 1999), stimulus-response compatibility effects are expected to occur in go-no-go tasks. This prediction is confirmed in two experiments in which subjects moved a hand to one side of the field on presentation of a go stimulus. Although the direction of movement was known in advance and the spatial attribute of the go stimuli was irrelevant to the go-no-go decision, the subjects' response time was shorter when the spatial attribute to the go stimulus corresponded to that of the response than when it did not. These effects are shown to depend on the similarity of the go and the no-go stimuli, as well as on whether the spatial attribute of the go stimuli was its actual location or its meaning. We discuss these results in terms of the temporal dynamics of automatic and controlled response processes, as hypothesized in the DO model.     

SPELLING AND EMERGENT PICTURE-PRINTED WORD RELATIONS ESTABLISHED WITH DELAYED IDENTITY MATCHING TO COMPLEX SAMPLES

Students with academic deficits learned delayed matching-to-sample tasks that used complex sample stimuli, each consisting of a picture and a printed word. A touch to the sample complex removed it from the computer display and produced either picture comparisons or a choice pool of letters. If the comparisons were pictures, selecting the picture identical to the preceding sample was reinforced. If the letters appeared, letter-by-letter construction of the preceding printed word sample was reinforced. The procedure engendered new constructed-response spelling performances and arbitrary relations among pictures and printed words in matching to sample. The emergence of relations among different sets of printed words (paired with the same pictures) suggested classes of equivalent stimuli. Outcome tests involving spoken words as sample stimuli suggested expansion of subjects' spelling repertoires and stimulus classes.     

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.     

A further examination of the lexical-processing stages hypothesized by the E-Z Reader model

Participants’ eye movements were monitored while they read sentences in which high- and low-frequency target words were presented normally (i.e., the normal condition) or with either reduced stimulus quality (i.e., the faint condition) or alternating lower- and uppercase letters (i.e., the case-alternated condition). Both the stimulus quality and case alternation manipulations interacted with word frequency for the gaze duration measure, such that the magnitude of word frequency effects was increased relative to the normal condition. However, stimulus quality (but not case alternation) interacted with word frequency for the early fixation time measures (i.e., first fixation, single fixation), whereas case alternation (but not stimulus quality) interacted with word frequency for the later fixation time measures (i.e., total time, go-past time). We interpret this pattern of results as evidence that stimulus quality influences an earlier stage of lexical processing than does case alternation, and we discuss the implications of our results for models of eye movement control during reading.