 PERGAMON Neuropsychologia 26 "0888# 620Ð633 9917!2821:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved PII]S9917!2821"87#99956!9 Facilitation and inhibition arising from the exogenous orienting of covert attention depends on the temporal properties of spatial cues and targets Paul Maru} a\b\c\ \ Murat Yucel b\c \ James Danckert b\c \ Geo} Stuart b \ Jon Currie b\d a School of Biophysics and Electrical Engineering\ Swinburne University of Technology\ Hawthorn\ Vic[\ Australia b The Neurophysiology and Neurovisual Research Unit\ Mental Health Research Institute of Victoria\ Parkville\ Vic[ 2941\ Australia c School of Psychological Science\ LaTrobe University\ Bundoora\ Vic[\ Australia d Brain Research Unit\ Drug and Alcohol Services\ Westmead Hospital\ Westmead\ Sydney\ Australia Received 14 November 0886^ accepted 4 May 0887 Abstract On the covert orienting of visual attention task "COVAT#\ responses to targets appearing at the location indicated by a non! predictive spatial cue are faster than responses to targets appearing at uncued locations when stimulus onset asynchrony "SOA# is less than approximately 199 ms[ For longer SOAs\ this pattern reverses and RTs to targets appearing at uncued locations become faster than RTs to targets appearing at the cued location[ This facilitation followed by inhibition has been termed the biphasic e}ect of non!predictive peripheral spatial cues[ Currently\ there is debate about whether these two processes are independent[ This issue was addressed in a series of experiments where the temporal overlap between the peripheral cue and target was manipulated at both short and long SOAs[ Results showed that facilitation was present only when the SOA was short and there was temporal overlap between cue and target[ Conversely\ inhibition occurred only when the SOA was long and there was no temporal overlap between cue and target[ The biphasic e}ect\ with an early facilitation followed by a later inhibition\ occurred only when the cue duration was _xed such that there was temporal overlap between the cue and target at short but not long SOAs[ In a _nal experiment\ the duration of targets the temporal overlap between cue and target and the SOA were manipulated factorially[ The results showed that facilitation occurred only when the SOA was short\ there was temporal overlap between cue and target and the target remained visible until the subject responded[ These results suggest that the facilitation and inhibition found on COVATs which use non!informative peripheral cues are independent processes and their presence and magnitude is related to the temporal properties of cues and targets[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ 0[ Introduction The covert orienting of visual attentional task "COVAT# developed by Posner ð08Ð13Ł has been in~uential in the development of cognitive neuropsychological theories of visual attention[ To measure exogenous attentional shifts\ the COVAT requires subjects to _x their eyes on a central location and to respond manually to the onset of a target in one of two peripheral locations either to the left or right of _xation[ An open box or circle marks these peripheral locations[ Before the target appears\ a spatial cue appears at one of the peripheral locations[ The target can then appear at the location indicated by the per!  Corresponding author[ Neurophysiology and Neurovisual Research Unit\ Mental Health Research Institute of Victoria\ Parkville\ Vic[ 2941\ Australia[ Tel[] ¦50!2!8277!0522^ fax] ¦50!2!8276!4950^ e!mail] paulÝneuro[mhri[edu[au ipheral cue "cued location# or at the location contralateral to the cue in the opposite visual _eld "uncued location#[ When the probability of targets appearing at the cued and uncued locations is equal\ the speed of reaction times to detect targets varies according to the location of the target "cued or uncued location# and the time interval between the onset of the cue and the onset of the target "stimulus onset asynchrony\ SOA# ð0\ 1\ 4\ 5\ 8\ 01Ð04\ 06Ð16\ 23Ð26Ł[ Converging evidence from single neuronal _ring rates in alert non!human primates\ neu! ropsychological studies of humans with focal brain lesions and neuroimaging studies of normal humans using the COVAT\ suggest that covert shifts of attention depend on the integrity of a distributed network of cort! ical and subcortical brain areas ð8\ 02\ 03\ 19Ð13\ 17\ 18Ł[ Despite the elegant simplicity of the COVAT\ there are still unresolved issues regarding the speci_c nature of re~exive attentional shifts[ One of the most long running