Phase correction in sensorimotor synchronization: nonlinearities in voluntary and involuntary responses to perturbations

When finger taps are synchronized with an auditory sequence, both a global phase shift (PS) and a local event onset shift (EOS) in the sequence elicit a phase correction response (PCR) on the next tap. The PCR to an expected PS is intended and large, whereas that to an expected EOS is unintended and smaller. PCR magnitude increases linearly with perturbation magnitude up to about +/-15% of the sequence period (500 milliseconds). With larger perturbations, voluntary PCRs increase more slowly whereas involuntary PCRs reach an asymptote. These results, obtained previously in a blocked design [J. Exp. Psychol. Human Percept. Perform. (in press)], were replicated in a randomized design and in two additional task contexts that varied participants' intentions while neutralizing their expectations. Neither design nor expectations seemed to play a role. However, considerable individual differences were noted. The results confirm that phase correction is partially automatic and partially subject to voluntary control, and they provide empirical estimates of error correction functions that may be useful in formal modeling of sensorimotor synchronization behavior.     

In support of Pockett's critique of Libet's studies of the time course of consciousness

Susan Pockett presents sound arguments supporting her reinterpretations of data that Libet and co-workers used to support a number of intriguing and influential conclusions regarding the microgenesis and timing of (a) conscious sensory experience and (b) volitionally controlled motor responses. The following analysis, extending and elaborating some of her main arguments, proposes that Libet's experimental methodologies and rationales, and thus also his interpretation of data, are flawed and that neglect or ignorance of methodological and empirical constraints well known to sensory psychologists risks drawing premature or faulty conclusions about the timing of conscious experience.     

A replication of Rorschach and MMPI-2 convergent validity

We replicated prior research on Rorschach and MMPI-2 convergent validity by testing 8 hypotheses in a new sample of patients. We also extended prior research by developing criteria to include more patients and by applying the same procedures to 2 self-report tests: the MMPI-2 and the MCMI-II. Results supported our hypotheses and paralleled the prior findings. Furthermore, 3 different tests for methodological artifacts could not account for the results. Thus, the convergence of Rorschach and MMPI-2 constructs seems to be partially a function of how patients interact with the tests. When patients approach each test with a similar style, conceptually aligned constructs tend to correlate. Although this result is less robust, when patients approach each test in an opposing manner, conceptually aligned constructs tend to be negatively correlated. When test interaction styles are ignored, MMPI-2 and Rorschach constructs tend to be uncorrelated, unless a sample just happens to possess a correlation between Rorschach and MMPI-2 stylistic variables. Remaining ambiguities and suggestions for further advances are discussed.     

Contents Volume 29 2000

Volume Contents

Contents Volume 29 2000     

Articulatory/phonetic sequencing at the level of the anterior perisylvian cortex: a functional magnetic resonance imaging (fMRI) study

Damage to the anterior peri-intrasylvian cortex of the dominant hemisphere may give rise to a fairly consistent syndrome of articulatory deficits in the absence of relevant paresis of orofacial or laryngeal muscles (apraxia of speech, aphemia, or phonetic disintegration). The available clinical data are ambiguous with respect to the relevant lesion site, indicating either dysfunction of the premotor aspect of the lower precentral gyrus or the anterior insula in the depth of the Sylvian fissure. In order to further specify the functional anatomic substratum of this syndrome, functional magnetic resonance imaging (fMRI) was performed during reiteration of syllables differing in their demands on articulatory/phonetic sequencing (CV versus CCCV versus CVCVCV). Horizontal tongue movements and a polysyllabic lexical item served as control conditions. Repetition of the CV and CCCV monosyllables elicited a rather bilateral symmetric hemodynamic response at the level of the anterior and posterior bank of the central sulcus (primary sensorimotor cortex), whereas a more limited area of neural activity arose within this domain during production of lexical and nonlexical polysyllables, significantly or exclusively lateralized toward the left hemisphere. There is neurophysiological evidence that primary sensorimotor cortex mediates the "fractionation" of movements. Assuming that the polysyllables considered are organized as coarticulated higher-order units, the observed restricted and lateralized cortical activation pattern, most presumably, reflects a mode of "nonindividualized" motor control posing fewer demands on "movement fractionation." These findings may explain the clinical observation of disproportionately worse repetition of trisyllabic items as compared to monosyllables in apraxia of speech. The various test materials failed to elicit significant activation of the anterior insula. If at all, only horizontal tongue movements yielded a hemodynamic reaction extending beyond the sensorimotor cortex to premotor areas. Since limbic projections target the inferior dorsolateral frontal lobe, the enlarged region of activation during horizontal tongue movements might reflect increased attentional requirements of this task.     

Auditory language comprehension: an event-related fMRI study on the processing of syntactic and lexical information

The functional specificity of different brain regions recruited in auditory language processing was investigated by means of event-related functional magnetic resonance imaging (fMRI) while subjects listened to speech input varying in the presence or absence of semantic and syntactic information. There were two sentence conditions containing syntactic structure, i.e., normal speech (consisting of function and content words), syntactic speech (consisting of function words and pseudowords), and two word-list conditions, i.e., real words and pseudowords. The processing of auditory language, in general, correlates with significant activation in the primary auditory cortices and in adjacent compartments of the superior temporal gyrus bilaterally. Processing of normal speech appeared to have a special status, as no frontal activation was observed in this case but was seen in the other three conditions. This difference may point toward a certain automaticity of the linguistic processes used during normal speech comprehension. When considering the three other conditions, we found that these were correlated with activation in both left and right frontal cortices. An increase of activation in the planum polare bilaterally and in the deep portion of the left frontal operculum was found exclusively when syntactic processes were in focus. Thus, the present data may be taken to suggest an involvement of the left frontal and bilateral temporal cortex when processing syntactic information during comprehension.     

Representation of subjective preferences under ambiguity

The objective of this paper is to show how potentially incomplete preferences of a decision maker (DM) on acts can be modelled formally in a subjective ambiguity perspective. We identify acts as functions from a state space Ω to bounded support (finitely additive) probabilities over a set X of prizes. Then, we characterize preferences over equibounded acts a which have a numerical representation by the family of functionals , where u is a cardinal utility on X (representing the risk attitude of the DM) and Π is a unique pointwise closed convex set of probabilities on all events in Ω (representing the ambiguity perceived by the DM). To this end, in addition to the usual independence and continuity assumptions, we add completeness and dominance for preferences restricted to constant acts; moreover, we consider two other properties (subjective monotonicity and coherence) related with the preferences of a DM who is not able, owing to his partial knowledge, to evaluate any event in Ω.     

The respective role of low and high spatial frequencies in supporting configural and featural processing of faces

One distinctive feature of processing faces, as compared to other categories, is thought to be the large dependence on configural cues such as the metric relations among features. To test the role of low spatial frequencies (LSFs) and high spatial frequencies (HSFs) in configural and featural processing, subjects were presented with triplets of faces that were filtered to preserve either LSFs (below 8 cycles per face width), HSFs (above 32 cycles per face width), or the full frequency spectrum. They were asked to match one of two probe faces to a target face. The distractor probe face differed from the target either configurally, featurally, or both featurally and configurally. When the difference was at the configural level, performance was better with LSF faces than with HSF faces. In contrast, with a featural difference, a strong performance advantage was found for HSF faces as compared to LSF faces. These results support the dominant role that LSFs play in the configural processing of faces, whereas featural processing is largely dependent on HSFs.     

An experimental study of the emergence of human communication systems

The emergence of human communication systems is typically investigated via 2 approaches with complementary strengths and weaknesses: naturalistic studies and computer simulations. This study was conducted with a method that combines these approaches. Pairs of participants played video games requiring communication. Members of a pair were physically separated but exchanged graphic signals through a medium that prevented the use of standard symbols (e.g., letters). Communication systems emerged and developed rapidly during the games, integrating the use of explicit signs with information implicitly available to players and silent behavior-coordinating procedures. The systems that emerged suggest 3 conclusions: (a) signs originate from different mappings; (b) sign systems develop parsimoniously; (c) sign forms are perceptually distinct, easy to produce, and tolerant to variations.