Biomedical subjects

M Valdés-Sosa

Publications and source records attributed to M Valdés-Sosa.

4 recordsLinked to original sources

PubMed2000

Different scalp topography of brain potentials related to expression and identity matching of faces.

Event-related potentials (ERPs) and behavioral data were recorded while subjects performed two tasks on the same set of faces (presented in pairs). One task was identity matching and the other expression matching. Two groups of subjects participated, one familiar and the other unfamiliar with the faces. Subjects were less accurate in matching expressions than identity. Familiarity facilitated identity but not expression matching. ERPs to mismatches in both tasks elicited a negativity around 400 ms, which was similar in latency and amplitude in the two tasks, but differed in scalp topography. Whereas the mismatch negativity had the same landscape over the left hemisphere for both tasks, the component related to expression had larger amplitudes over the right-temporal regions. Familiarity had no effect on these negativities, although it affected a late positivity (LP). These results support the idea of distinct neural systems subserving face processing, and agree with a role of the right hemisphere for the processing of emotional expressions.

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PubMed2000

Making features relevant: learning faces and event-related potentials recording using an analytic procedure.

We present a procedure designed for the learning of faces (represented by realistic drawings) and a task for the subsequent recording of Event-Related Potentials (ERPs), with the aim of investigating the psychobiological mechanisms involved in the recognition of familiar (or known) faces. The learning procedure consisted in a series of six sessions in which subjects familiarized themselves with the faces through a forced-choice features task: after the study of a set of 40 faces, each of these was presented at random in an incomplete way (without the eyes/eyebrows fragment), together with two sets of eyes and eyebrows for the subject to decide which of them corresponded to each face. This procedure is thought to facilitate for subjects the acquisition of the information related to the structural description of the faces (that is, without associated verbal/semantic information) using preferentially analytic processing strategies. The parameter d' of the Theory of Signal Detection allowed us to evaluate in the course of the learning sessions the degree of familiarization achieved with the studied faces. Subsequently, an ERPs' recording session was carried out, during which subjects executed a face-feature matching task. In this task, similar in structure to that carried out in the learning sessions, the subject had to decide whether the automatic completion of the faces that was made was correct or incorrect. ERPs' effects related to mismatching features were obtained, which indicate the existence of specific cerebral mechanisms involved in the recognition of faces.

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PubMed1994

An ERP study of expectancy violation in face perception.

Expectancies about face-structure can be induced by viewing parts of faces, which generates constraints due to two types of knowledge: feature-content and configuration. In a first experiment ERPs were recorded when parts of familiar faces were completed with incongruent features (from another face), as opposed to congruent features (from the same face). All features were in the correct configuration. An enhanced negativity was found for incongruent completions (N374) that was larger over the right side of the scalp. This replicates the results of Valdes-Sosa and Bobes (1990). In another two experiments, ERPs were recorded when parts of familiar faces were completed by congruent features, but sometimes placed in an incorrect position. In one experiment the features were jumbled; in the other, the features were slightly displaced. These configuration distortions were associated to late positive components, with a maxima at the centro-parietal region, of equal amplitude for both kinds of configuration anomalies. The N374 component seems to be a non-linguistic analog of the N400. The different ERP signatures for expectancy violations of configuration and feature-content suggest that these types of information are processed separately at some stages.

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PubMedDate not supplied

[Visual extinction: a study by means of potentials evoked with movement].

INTRODUCTION: The term extinction refers to the phenomenon in which a patient with a lesion of the central nervous system ignores one of two stimuli in conditions of simultaneous bilateral stimuli. Various studies observe this phenomenon as the expression of a deficit in the process of selective attention, but there are few studies with potentials related to events (PRE). OBJECTIVES: To find the possible electrical correlation of the extinction phenomenon and the stage of processing at which this occurs. PATIENTS AND METHODS: We studied a patient with a right parieto occipital lesion and a control person of the same race, age, sex and educational level. We carried out two experiments. The first of these was to determine the direction of movement of two surfaces with red and green spots situated on both sides of a central fixation point. In the second experiment, the same task was carried out, but the two surfaces were superimposed, in the same place. In both cases the first movement occurred in the surface which was being attended to and the second might be this surface or the other. The proportion of correct answers were recorded for both movements. The PRE showed an attention disorder which affected the spatial distribution of attention with conservation of the attention to objects. CONCLUSIONS: The suppression of the P1 N1 components are the electrical correlate of the phenomenon of extinction which should occur during early stages of processing. Further investigations are necessary in a larger number of cases.

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