Sequential Effects in Spatial Exogenous Cueing: Theoretical and Methodological Issues

Sequential Effects in Spatial Exogenous Cueing: Theoretical and Methodological Issues Alessandro Couyoumdjian (alessandro.couyoumdjian@uniroma1.it) Faculty of Psychology 1, University “La Sapienza” via dei Marsi 78 - 00185 Rome ITALY Roberto Baiocco (roberto.baiocco@uniroma1.it) Faculty of Psychology 1, University “La Sapienza” via dei Marsi 78 - 00185 Rome ITALY Carlamaria Del Miglio (carlamaria.delmiglio@uniroma1.it) Department of Psychology, University “La Sapienza”, via dei Marsi 78 - 00185 Rome ITALY (SOAs) are longer than 200-300 ms, an inhibition effect is observed (IOR; performance on invalid trials is better than performance on valid trials) (Posner & Cohen, 1984). Facilitation effects are often interpreted consistently with the hypothesis that on valid trials cues have involuntary captured attention and then targets appear on the location currently “illuminated” by the attentional spotlight. Differently, inhibition effects are explained consistently with the hypothesis that attentional focus is more probably located on locations that are not recently scanned (Klein, Even though such effects are very often interpreted as caused by spatial orienting of attention, they seem to be analogous to first order sequential effects usually observed in two-choice tasks (Bertelson, 1961; Soetens, 1998). An extensive number of two-choice task experiments have showed that reaction time (RT) to a stimulus is dependent not only on that stimulus but also on the sequence of preceding stimuli. Influences caused by the previous stimulus-response cycle are called “first order sequential effects”, while influences caused by earlier cycles are called “higher order sequential effects”. Similarly to cueing experiments, in two-choice tasks the sequential effects mainly depend on response-stimulus intervals (RSI). Infact, first order repetition effects are usually observed with relatively short RSIs (less than 500 ms); whereas, first order alternation effects are observed with relatively long RSIs (i.e., RTs are faster to a different stimulus than to a repeated stimulus). While repetition effects are often explained in terms of an automatic facilitation caused by a residual activation of memory traces, alternation effects are associated to a kind of subjective expectancy. More specifically, in a series of binary stimuli subjects seem to expect more alternations than repetitions; this phenomenon is well known as “gambler’s fallacy” and it is often explained in terms of an erroneous representation of randomness and probability (Nickerson, 2002) based on what Tversky and Kahneman (1971) called “law of small numbers” (which is the erroneous belief that proprieties of Abstract Spatial cueing is a largely used experimental paradigm to study exogenous attention orienting, both in behavioural and neurological research. In such a paradigm participants are presented a sequence of trials that are assumed to be independent from each other. In each trial a peripheral spatial cue is presented, followed by a target peripheral stimulus; subjects are required to respond as fast as possible to targets, attempting to ignore cues. In such experiments RTs are mainly dependent to trial type (valid vs invalid) and to Cue- target intervals (short vs long). The present study aims at investigating the hypothesis that facilitation and inhibition effects, observed in cueing experiments, can be considered analogous to sequential effects, usually observed in two- choice tasks, and then that all these effects can be explained by the very same cognitive mechanisms. Results from two cueing experiments support this theoretical explanation and highlight the relevance of taking into account sequential effects. Introduction In the study of visuospatial attention endogenous and exogenous control modalities are recognized. Probably, spatial cueing is the most used experimental paradigm to investigate the mechanisms and characteristics of both voluntary and automatic attention orienting (Posner, 1980). In such a simple paradigm a sequence of trials is administered to the subjects; each trial consists of two consecutive events: the presentation of a spatial cue followed by the presentation of a target stimulus, to which subjects are required to respond as fast as possible. To study the exogenous modality, usually cues are peripheral stimuli that are unpredictably presented on the same location of the following target or on a different location. While in the former case the trial is called “valid”, in the latter case the trial is called “invalid”. Typically, when the intervals between cues and targets (SOAs) are shorter than 200-300 ms, a facilitation effect is observed (performance on valid trials is better than performance on invalid trials); on the contrary, when the intervals between cues and targets