Raffaella I. Rumiati

Neural basis of pantomiming the use of visually presented objects

UNLABELLED Neuropsychological studies of patients suffering from apraxia strongly imply a left hemisphere basis for skillful object use, the neural mechanisms of which, however, remain to be elucidated. We therefore carried out a PET study in 14 healthy human volunteers with the aim to isolate the neural mechanisms underlying the sensorimotor transformation of object-triggers into skilled actions. We employed a factorial design with two factors ( RESPONSE naming, pantomiming; and TRIGGER: actions, objects) and four conditions (IA: imitating the observed pantomime; IO: pantomiming the use of the object shown; NA: naming the observed pantomime; NO: naming the object shown). The design thus mainly aims at investigating the interaction [i.e. (IO-IA)-(NO-NA)] which allows the assessment of increased neural activity specific to the sensorimotor transformation of object-triggers into skilled actions. The results (P < 0.05, corrected) showed that producing a wide range of skilled actions triggered by objects (controlled for perceptual, motor, semantic, and lexical effects) activated left inferior parietal cortex. The data provide an explanation for why patients with lesions including left parietal cortex suffer from ideational apraxia as assessed by impaired object use and pantomining to visually presented objects.

What is the role of motor simulation in action and object recognition? Evidence from apraxia

An important issue in contemporary cognitive neuroscience concerns the role of motor production processes in perceptual and conceptual analysis. To address this issue, we studied the performance of a large group of unilateral stroke patients across a range of tasks using the same set of common manipulable objects. All patients (n = 37) were tested for their ability to demonstrate the use of the objects, recognize the objects, recognize the corresponding object-associated pantomimes, and imitate those same pantomimes. At the group level we observed reliable correlations between object use and pantomime recognition, object use and object recognition, and pantomime imitation and pantomime recognition. At the single-case level, we document that the ability to recognize actions and objects dissociates from the ability to use those same objects. These data are problematic for the hypothesis that motor processes are constitutively involved in the recognition of actions and objects and frame new questions about the inferences that are merited by recent findings in cognitive neuroscience.

Common and Differential Neural Mechanisms Supporting Imitation of Meaningful and Meaningless Actions

Neuropsychological studies indicate that, after brain damage, the ability to imitate meaningful or meaningless actions can be selectively impaired. However, the neural bases supporting the imitation of these two types of action are still poorly understood. Using PET, we investigated in 10 healthy individuals the neural mechanisms of imitating novel, meaningless actions and familiar, meaningful actions. Data were analyzed using SPM99. During imitation, a significant positive correlation (p < .05, corrected) of regional cerebral blood flow with the amount of meaningful actions was observed in the left inferior temporal gyrus only. In contrast, a significant positive correlation (p < .05, corrected) with the amount of meaningless movements was observed in the right parieto-occipital junction. The direct categorical comparison of imitating meaningful (100) relative to meaningless (100) actions showed differential increases in neural activity (p < .001, uncorrected) in the left inferior temporal gyrus, the left parahippocampal gyrus, and the left angular gyrus. The reverse categorical comparison of imitating meaningless (100) relative to meaningful (100) actions revealed differential increases in neural activity (p < .001, uncorrected) in the superior parietal cortex bilaterally, in the right parieto-occipital junction, in the right occipital-temporal junction (MT, V5), and in the left superior temporal gyrus. Increased neural activity common to imitation of meaningless and meaningful actions compared to action observation was observed in a network of areas known to be involved in imitation of actions including the primary sensorimotor cortex, the supplementary motor area, and the ventral premotor cortex. These results are compatible with the two-route model of action imitation which suggests that there are at least two mechanisms involved in imitation of actions: a direct mechanism transforming a novel action into a motor output, and a semantic mechanism, on the basis of stored memories, that allows reproductions of known actions. Our results indicate that, in addition to shared neural processes, the direct and the semantic mechanisms that underlie action imitation also draw upon differential neural mechanisms. The direct mechanism underlying imitation of meaningless actions differentially involves visuospatial transformation processes as evidenced by activation of areas belonging to the dorsal stream. In contrast, imitation of meaningful actions differentially involves semantic processing as evidenced by activation of areas belonging to the ventral stream.

A form of ideational apraxia as a selective deficit of contention scheduling

In this paper we studied three brain-damaged patients: the first two, DR and FG, had limb apraxia whilst the third was a control patient (WH2) with an executive function disorder but without limb apraxia. DR and FG were impaired in carrying out everyday actions, whilst they maintained the ability to sequence photographs representing those same activities. The failure in the action production task was not caused by visual agnosia for objects, as the patients could recognise them from sight. Nor was it produced by a loss of knowledge about their functions (De Renzi & Lucchelli, 1988), as DR and FG could identify objects from descriptions of their use. WH2s pattern of performance doubly dissociated from that of the apraxic patients, namely spared action production on the multiple object test, but faulty sequencing of photographs. WH2s difficulties in sequencing photographs were not due to a failure to understand the task, as she could sequence stimuli other than actions (e.g., shapes and numbers). Nor were the differences due to a loss of knowledge about the actions, since she could perform and identify them from photographs. These results show that the kind of apraxia observed in DR and FG is not produced by a degraded action sequence representation (Lehmkuhl & Poeck, 1981; Poeck & Lehmkuhl, 1980). We interpreted our results within a contention scheduling model (Cooper & Shallice, 2000; Norman & Shallice, 1986).

Recognition by action: dissociating visual and semantic routes to action in normal observers.

In this article the operation of a direct visual route to action in response to objects, in addition to a semantically mediated route, is demonstrated. Four experiments were conducted in which participants made gesturing or naming responses to pictures under deadline conditions. There was a cross-over interaction in the number of visual errors relative to the number of semantic plus semantic-visual errors in the two tasks: In gesturing, compared with naming, participants made higher proportions of visual errors and lower proportions of semantic plus semantic-visual errors (Experiments 1, 3, and 4). These results suggest that naming and gesturing are dependent on separate information-processing routes from stimulus to response, with gesturing dependent on a visual route in addition to a semantic route. Partial activation of competing responses from the visual information present in objects (mediated by the visual route to action) leads to high proportions of visual errors under deadline conditions. Also, visual errors do not occur when gestures are made in response to words under a deadline (Experiment 2), which indicates that the visual route is specific to seen objects.

The strategic control of multiple routes in imitation of actions.

The aim of this study was to bring to the surface the strategic use of imitative processes in the context of a 2-route model: (a) direct imitation, used in reproducing new, meaningless actions, and (b) imitation based on stored semantic knowledge of familiar meaningful actions. Three experiments were carried out with healthy participants who reproduced meaningful and meaningless actions within an established time limit. The study investigated 3 factors that could potentially affect the selection of processes used for imitation: (a) the composition of the experimental list (blocked or mixed presentation), (b) the presence-absence of instructions (Experiments 1 and 2), and (c) the relative proportions of the stimuli (Experiment 3). Overall, the results suggest that each of these factors influences the selection of imitative strategies in healthy individuals with temporarily reduced capacities, as happens in the case of brain-damaged patients.

Imitation of novel and well-known actions: the role of short-term memory.

Abstract. Four experiments were carried out using the action span paradigm. In experiment 1 we found that well-learnt, meaningful (MF) actions were imitated better than novel, meaningless (ML) actions. In experiments 2 and 3, during the encoding of MF and ML actions, participants were required to carry out different suppression tasks. In experiment 2 we replicated the advantage of MF actions over ML actions and also found that the motor suppression shortened the action span more than the other forms of suppressions (spatial and articulatory). Action encoding and motor suppression tapping the same subsystem, temporarily holding the motor information, could explain the reduced motor span obtained in experiment 2. Two alternative explanations that could have accounted for this effect were ruled out in experiments 3 and 4. In experiment 3 we verified whether the reduction of the action span was produced by the different combination of the articulatory suppression with motor suppression or with the spatial suppression. In experiment 4, we demonstrated that the reduction was not due to the motor suppression being more difficult than the other types of suppression. The critical finding that the spans of well-learnt, MF actions are longer than those of novel, ML actions observed in experiments 1 and 2 was interpreted in terms of different processing routes engaged in the imitation of these two types of actions. MF actions can be imitated along both a semantic, indirect route and a direct route leading from the visual analysis of the action to the motor system. In contrast, the imitation of ML actions is accomplished along the direct route only.

The selective impairment of the phonological output buffer

A single case study is presented of a patient, LT, with a reproduction conduction aphasic pattern of performance on word reproduction tasks; thus he made substitutions, insertions, deletions, and transpositions in reading, writing, and repetition of words and nonwords, as well as in sentence production, and in spoken and written picture and action naming. Further analyses revealed that there was no effect of semantic or syntactic structure on performance, and that reading was slightly better than repetition and writing. Finally, the observed effects of lexicality, length, and word frequency were similar to those found in other phonological output buffer patients. Overall, the pattern observed fits the characteristics typical of phonological output buffer patients, as characterised by Caramazza, Miceli, and Villa (1986). We discuss the implications of these results for understanding the role of the output phonological buffer in neuropsychological and computational models of writing, reading, and repetition. From the perspective of LT’s performance, the hypothesis suggested by Caramazza et al. (1986), and that of Hartley and Houghton (1996), that word production in reading and repetition uses an additional route to access articulatory or phoneme-level representations from the phonological output lexicon, is unnecessary; instead, word-nonword differences in other patients can be attributed to resource demand differences between the two types of stimuli. LT’s preserved span fit with the assumption that two phonological buffers exist, one for input and the other for output. Results from a word repetition experiment, in which word syllable structure was manipulated, are in conflict with one further noncentral aspect of the Hartley and Houghton’s model, which otherwise fits the results well.

AGNOSIA WITHOUT PROSOPAGNOSIA OR ALEXIA: EVIDENCE FOR STORED VISUAL MEMORIES SPECIFIC TO OBJECTS

A single-case study is presented of a patient w ith a modality-specific problem in visual object recognition, w hich can be linked to impaired stored descriptions for objects. Performance was poor on tasks requiring naming, semantic decisions, and object decisions to seen objects. Performance on semantic decisions w ith w ords, however, was relatively good, demonstrating that the problem was not due solely to a general semantic impairment. Moreover, in contrast to the impairments in visual object recognition, both face recognition and on-line visual word recognition w ere within normal limits. The data indicate that im pairments of object recognition can be distinguished from impairments of face and visual w ord recognition, even when the problem can be localised within the structural description system for objects. We discuss the im plications of the results for understanding the relations between object, face, and word identification.

Equality versus self-interest in the brain: Differential roles of anterior insula and medial prefrontal cortex

Everything else being the same, an equal outcome is generally preferred; however, an equitable allocation sometimes is possible only by sacrificing the total amount of resources available to society. Moreover, direct interests may interact with the perception of equality. Here, we have investigated individual preferences, and their neural basis, by employing a task in which an allocation of a fixed amount between the subject and another person (MS condition) or two third parties (TP condition) is randomly determined. The subject can accept or reject the outcome, in the same fashion as the Ultimatum Game: thus an unequal offer may be rejected at the cost of a loss in total amount. Behavioral results show preference for equal outcomes in TP and for equal and advantageous outcomes in MS. An activation of medial prefrontal cortex (mPFC), extending to the anterior middle cingulate cortex (aMCC), was found in MS unequal outcomes, particularly for disadvantageous outcomes and consequent rejections. The anterior insula (AI) was active for unequal outcomes, in both MS and TP. We propose that the equal treatment is a default social norm, and its violation is signaled by the AI, whereas aMCC/mPFC activation, negatively correlated to rejections, reflects the effort to overcome the default rule of equal treatment in favor of a self-advantageous efficiency.