A.B. Watson / Vision Research 38 (1998) 1619–1621 1621 [7] Watson AB, Turano KA. The optimal motion stimulus. Vis Res 1995;35:325 – 36. [8] Garcia-Perez MA, Sierra-Vazquez V. The optimal motion stimulus: comments on Watson and Turano (1995). Vis Res 1998;38:1611 – 1619. [9] Watson AB, Thompson PG, Murphy BJ, Nachmias J. Sum- mation and discrimination of gratings moving in opposite di- rections. Vis Res 1980;20:341 – 7. [10] Anderson SJ, Burr DC. Spatial summation properties of direc- tionally selective mechanisms in human vision. J Opt Soc Am 1991;8:1330 – 9. [11] Anderson SJ, Hess RF. Post-receptoral undersampling in nor- mal human peripheral vision. Vis Res 1990;30:1507 – 15. PII:S0042-6989(97)00355-6 On the time course of exogenous cueing effects: a commentary on Tassinari et al. (1994) Juan Lupia ´n ˜ ez *, Bruce Weaver School of Psychology, Uniersity of Wales, Bangor, Gwynedd LL57 2DG, UK Received 25 March 1997; received in revised form 19 May 1997 In their classic paper, Posner and Cohen [1] studied the time course of the attentional effect of uninforma- tive peripheral cues. In the first experiment they de- scribe, one of three horizontally aligned boxes (each 1° ×1° of visual angle in size) was cued with a 150 ms brightening of its outline. At a variable SOA of 0, 50, 100, 200, 300 or 500 ms the target (a 0.1° filled square) was displayed inside one of the boxes and subjects were to detect it as quickly as possible by pressing a single key. Responses were faster when cue and target appeared in the same location than when they appeared in opposite locations, but only if the cue-target SOA was less than 200 ms. With longer SOAs, the pattern was reversed: That is, responses were slower when cue and target appeared in the same location. Posner and Cohen argued that the early facilitation for cued targets was automatic in nature, and that after a short interval it was counter- acted by an inhibitory effect. This inhibitory effect was due to attention being inhibited from returning to previously explored locations — hence the name ‘in- hibition of return’ (IOR) — and ‘evolved to maximise sampling of the visual environment’ (p. 550). Similar results have been reported by Maylor [2] and Maylor and Hockey [3]. Recently, this time course of the attentional effect of uninformative cues (i.e. first facilitation and then inhibition) has been challenged. According to Tassi- nari et al. [4], ‘inhibition does not follow facilitation, as envisioned by Maylor [2], but precedes and over- laps with it’ (p. 187). There are two parts to this statement: First, it is claimed that the inhibitory effect precedes the facilitatory effect; and second, that the inhibitory and the facilitatory effects overlap in time. We do not dispute the second of these claims. Posner and Cohen [1] were first to suggest that peripheral cues have both facilitatory and inhibitory effects, and that these effects overlap in time. Tipper et al. [5] have made the same suggestion, and we concur with this view. We do not agree with the first claim, how- ever, and will attempt to explain why not in what follows. Tassinari et al. [4] base their claims, especially the first one, on the results they obtained in a series of four experiments that included a 0 ms cue-target SOA condition. We contend that the results of this 0 SOA condition suffer from very serious methodological problems, and that the authors are in no position to support their claim that inhibition precedes facilita- tion. In Tassinari et al.’s (1994) paper the target to be detected was a 0.5° ‘greenish’ filled square, which could be displayed inside one of four 1.2° (or 2°) boxes aligned on the horizontal axis, two to the right and two to the left of fixation (at 4° and 12°). Before the target was displayed, one of the boxes was cued 0, 65, 130, 300 or 900 ms before target appearance. Apart from SOA, the other independent variable in the experiments was Cueing, with three levels: SP (cue and target appeared at the same point), SF (they ap- peared in the same field), and OF (they appeared in opposite fields). The target was always displayed for 16 ms, and the duration of the cue was manipulated between experiments. (Cue durations were 16 ms and 300 ms in experiments 1 and 2, respectively; and 130 ms in experiments 3 and 4). The main result was that in all experiments, 0 ms SOA responses were slower in the SP condition than in OF. Depending on cue duration, this negative ef- fect (inhibition?) either disappeared or turned into a positive effect (facilitation) at an intermediate SOA. * Corresponding author. E-mail: j.lupiane@platon.ugr.es.