ELSEVIER Electroencephalography and clinical Neurophysiology 95 (1995) 277-292 o ERP signs of early selective attention effects to check size A. Zani a,*, A.M. Proverbio b lstituto di Psicologia, Consiglio Nazionale delle Ricerche, Viale Marx 15, O0137 Rome, Italy b Dipartimento di Psicologia Generale, Unit,ersith di Padova, Padua, Italy Accepted for publication: 3 April 1995 Abstract In ERP literature on visual selective attention evidence has been provided that selectively directing attention to a spatial frequency affects the visual processing of the attended frequency, and of unattended frequencies within the same channel bandwidth, starting at a relatively late level of post-stimulus processing, i.e., after about 150 msec. Nevertheless, little knowledge is available about the topographic distribution of these attention effects. This study investigated attentional selection of stimulus relative size at occipital and latero-occipital sites, as well as at fronto-lateral sites. ERPs from posterior scalp electrode sites showed that attention to check sizes enhanced the early sensory components, thus indicating that feature-based attention may result in a modulation of sensory processing. Comparisons of the ERPs to relevant and irrelevant patterns showed an enhanced latero-occipital Pgo positivity as well as an occipital Nll 5 negativity to relevant patterns, thus also suggesting possible differential mechanisms of early attentional selectivity at these locations. Later effects of attention consisted of a selection negativity to relevant patterns at posterior electrodes, and a selection positivity at latero-frontal sites. A larger late positivity to irrelevant patterns at anterior sites also suggested an active suppression of attentional response to irrelevant information. Moreover, right-and left-sided asymmetries were found to be respectively consistent for the Pgo and N115 with left hemispheric specialization for high, and right hemispheric specialization for low spatial frequencies. A stronger left-sided attentional selectivity has also been found. Keywords: Early selective attention; Event-related potentials; Spatial frequency channels; Hemispheric asymmetries; Arousal I. Introduction It is generally acknowledged that object recognition is accomplished through the decomposition of the visual image into its spatial frequency components (Kulikowski et al., 1982; Ginsburg, 1986). Strong neurophysiological support for this spatial frequency filter model of vision has come from the demonstration of: (1) the spatial frequency selectivity of single cells in mammalian visual cortex (Maffei and Fiorentini, 1973; De Valois et al., 1978), and (2) the organization of cells with a similar spatial fre- quency selectivity (e.g., a similar receptive field organiza- tion) in columns forming a neuro-anatomical substrate for the independent size-specific sensitive channels proposed * Corresponding author. Tel.: + 39 6 86090224; Fax: + 39 6 824737; E-mail: Zani@kant.irmkant.rm.cnr.it. at the very outset by Blakemore and Campbell (1969) and Campbell and Maffei (1970). Thus, the analysis of visual information into its spatial frequency components has gained popularity as a tool for understanding the function- ing of the visual system. However, with few exceptions, most of the research adopting this model of spatial vision based on a multiple size-tuned channel approach has pro- gressed with the implicit bottom-up assumption that these channels unselectively take in all aspects of the stimulus presented to them. Conversely, relatively few attempts have been made to relate these size-specific channels to stimulus selection mechanisms. Harter and Previc (1978) first attempted to assess the effects of selective attention on the activity of cortical size channels, or how selectively a relevant size-specific pattern could be attended. They found an increase in amplitude of the selection negativity (SN) to check sizes attended and responded to, which generalized to adjacent check sizes. 0013-4694/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0013-4694(95)00078-X EEG 93718