Neural Site of the Redundant Target Effect: Electrophysiological Evidence

Abstract

n The present study represents an attempt to nd an electrophysiological correlate of the redundant targets effect, or RTE (i.e., the speeding up of reaction time, or RT, for redundant vs. single targets). Subjects made a speeded response either to one small checkerboard presented to the left or right of xation or to a pair of identical checkerboards presented simultaneously to both hemi elds. Both single and double targets could appear either in the upper or lower visual hemi eld. The task required detection but not discrimination of the stimuli. During task performance, we recorded the event-related potentials (ERPs) elicited by the checkerboard targets. As in previous studies, we found that manual RTs to bilateral stimuli were faster than those to unilateral stimuli. This effect was more marked for lower-than for upper-eld stimuli and could not be ascribed to probability summation. In addition, we found that the P1 and N1 components of the visual ERP had a shorter latency for bilateral than for summed unilateral stimuli presented to the two hemi elds. In parallel with the behavioral ndings, the latency values for the above components showed a larger RTE for lower-eld stimuli. These ndings indicate that the RTE occurs at the level of early visual processing, probably in the extrastriate visual cortex, rather than at late decisional or premotor stages. n

Auditory–Visual Multisensory Interactions in Humans: Timing, Topography, Directionality, and Sources

“…Our analyses here are based on the application of an additive model to detect nonlinear neural response interactions, wherein the ERP in response to the AV S condition is contrasted with the summed ERPs in response to the A S and V S conditions (hereafter referred to as "pair" and "sum" ERPs, respectively). Such a model has been repeatedly applied in ERP and magnetoencephalography studies in humans (Miniussi et al, 1998;Giard and Peronnet, 1999;Foxe et al, 2000;Murray et al, 2001Murray et al, , 2005Molholm et al, 2002;Besle et al, 2004;Möttönen et al, 2004;Brefczynski-Lewis et al, 2009;Sperdin et al, 2009Sperdin et al, , 2010Raij et al, 2010) as well as electrophysiological investigations in nonhuman primates (Meredith and Stein, 1986;Stein and Meredith, 1993;Wallace et al, 1996;Wallace and Stein, 2007;Kayser et al, 2008). Despite its widespread application, this model nonetheless receives some criticism (Gondan and Röder, 2006), which has been refuted on theoretical and empirical grounds (Fort et al, 2002a;Besle et al, 2004).…”

Functional asymmetry and interhemispheric cooperation in the perception of emotions from facial expressions

“…In normal viewers the RTE has also been demonstrated with meaningful stimuli such as words (Hasbrooke and Chiarello 1998;Mohr et al 1996), numbers (Ratinckx and Brysbaert 2002), drawings of animals or objects (Koivisto 2000), and familiar neutral faces (Mohr et al 2002). Likewise, direct tests have often shown violations or race models, thereby providing support for models based on neural coactivation and interhemispheric summation (Corballis 2002;Grice and Reed 1992;Iacoboni et al 2000;Iacoboni and Zaidel 2003;Marzi et al 1996;Miller 1982Miller , 1986Miniussi et al 1998;Mordkoff and Yantis 1993;Reuter-Lorenz et al 1994;Savazzi and Marzi 2002).…”

“…Clearly, with two targets contributing activation toward the same threshold, the response is activated more rapidly than when there is only one target contributing activation. Although the concept of coactivation originally proposed by Miller (1982Miller ( , 1986 was not necessarily linked to neural activity, several more recent studies on brain-damaged patients and with neuroimaging techniques have argued convincingly that it is equivalent of neural summation and interhemispheric interaction (Corballis 1998;Corballis et al 2002Corballis et al , 2003Iacoboni et al 2000;Iacoboni and Zaidel 2003;Marzi et al 1996;Miniussi et al 1998;Reuter-Lorenz et al 1994;Corballis 2002, 2003;Savazzi and Marzi 2002).…”

“…For instance, the RTE has been shown using simple flashes (Corballis 2002;Savazzi and Marzi 2002), checkerboards (Miniussi et al 1998), shapes and colours (Mordkoff and Yantis 1993), letters (Grice and Reed 1992;Mordkoff and Miller 1993), and letterstrings (Marks and Hellige 1999), on healthy subjects as well as on neurological patients (with hemianopia and blindsight: de Gelder et al 2001;Marzi et al 1986;hemispherectomy: Tomaiuolo et al 1997;split-brain: Corballis 1995;Forster and Corballis 2000;Iacoboni et al 2000;Mohr et al 1994;Reuter-Lorenz et al 1994;Corballis 2002, 2003;and visual extinction: Marzi et al 1996). In normal viewers the RTE has also been demonstrated with meaningful stimuli such as words (Hasbrooke and Chiarello 1998;Mohr et al 1996), numbers (Ratinckx and Brysbaert 2002), drawings of animals or objects (Koivisto 2000), and familiar neutral faces (Mohr et al 2002).…”

Interest and validity of the additive model in electrophysiological studies of multisensory interactions

“…The [AV-(A+V)] complex was used to determine cortical regions that were uniquely activated by polysensory stimulation." (Barth et al, 1995 p.179) Although this model theoretically can be applied to any measures of human brain activity, it has been mainly used in electrophysiological data (scalp ERP and magneto-encephalography, MEG: Miniussi et al, 1998;Giard & Peronnet, 1999;Foxe et al, 2000;Raij et al, 2000;Fort et al, 2002aFort et al, , 2002bMolholm et al, 2002;Klucharev et al, 2003;Möttönen et al, 2004). On the other hand, its use has been recurrently criticized (Teder-Sälejärvi et al, 2002;Calvert & Thesen, in press) because of the multiple biases it can generate in the estimation of the crossmodal interactions if several important conditions are not fulfilled.…”