Academic journal article The Spanish Journal of Psychology

Hemispheric Differences for Global and Local Processing: Effect of Stimulus Size and Sparsity

Academic journal article The Spanish Journal of Psychology

Hemispheric Differences for Global and Local Processing: Effect of Stimulus Size and Sparsity

Article excerpt

The present experiment was designed to assess the hemispheric differences for global and local processing in healthy participants under different conditions of stimuli visibility, by means of varying the size and sparsity. Three different sizes and three different matrixes of hierarchical stimuli were introduced. Stimuli consisted of incomplete squares with one side missing. Participants were asked to carry out an orientation classification task (left/right), indicating the orientation of the square opening either at global or local levels. The results do not support the hemispheric differences for global and local processing, showing the same efficiency of right and left hemispheres for analyzing global and local information. Nevertheless, other results found are consistent with the hypothesis of right hemisphere superiority under degraded stimulus conditions.

Keywords: global processing, local processing, hemispheric asymmetries, hemispheric specialization, task demands

El objetivo del presente experimento ha sido analizar las diferencias hemisféricas en el procesamiento global y local de la información visual en participantes con cerebro intacto bajo diferentes condiciones de visibilidad del estímulo, Se introdujeron estímulos jerárquicos consistentes en cuadrados abiertos hacia la derecha o izquierda, variando el tamaño (3.23°, 6.44° y 9.61°) y la densidad estimular (matrices de 4×4, 5×5 y 6×6 elementos). Los participantes llevaron a cabo una tarea de clasificación de la orientación (izquierda/derecha), indicando la orientación de la apertura en el nivel global o en el local. Los resultados no muestran evidencias que apoyen la diferenciación hemisférica en el procesamiento global y local, aunque fueron consistentes con la hipótesis de una superioridad de hemisferio derecho bajo condiciones de degradación estimular.

Palabras clave: procesamiento global, procesamiento local, asimetría hemisférica, especialización hemisféricas, demanda de la tarea

The hypothesis of global precedence was enunciated by Navon (1977, 1981) stating that the processing of a visual form takes place hierarchically and sequentially, from global features to local ones. In his experiments, hierarchical stimuli were used, that is, large figures, which represent the global level, made up of smaller ones, which represent the local level. According to this hypothesis, two experimental results should be found in the research: global advantage and global interference. The first occurs when the global level is identified more quickly and more accurately than the local one. The second implies that global identity interferes when the local level is analyzed but local identity does not interfere when the global one is analyzed.

Subsequent research with hierarchical stimuli has demonstrated that global and local levels can be processed in parallel (Hoffman, 1980; Kinchla, Solis-Macias, & Hoffman, 1983; Miller, 1981a, 1981b) and that global advantage and interference can be either attenuated or modified to local advantage depending on several experimental conditions. For this reason, the term dominance instead of precedence has been proposed (Blanca, Luna, López-Montiel, Rando, & Zalabardo, 2001).

Hierarchical stimuli have also been used to study the functional hemispheric specialization for global and local processing. A superiority of right hemisphere (RH) for global processing and a superiority of left hemisphere (LH) for local one has been found in studies with brain-damaged patients (Delis, Robertson, & Efron, 1986; Hickok, Kirk, & Bellugi, 1998; Lamb, Robertson, & Knight, 1989; Robertson & Delis, 1986; Robertson, Lamb & Knight, 1988), and with healthy participants using positron emission tomography and functional magnetic resonance (Fink et al., 1996, 1997; Martínez et al., 1997). Delis et al., (1986) found that participants with lesions in the RH and LH had more difficulty in drawing and remembering the global and local form of the visual pattern, respectively. …

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