Academic journal article Canadian Journal of Experimental Psychology

Spatial Coding and Central Patterns: Is There Something Special about the Eyes?

Academic journal article Canadian Journal of Experimental Psychology

Spatial Coding and Central Patterns: Is There Something Special about the Eyes?

Article excerpt


In this study we investigated in a Simon-like task whether task-irrelevant spatial information, delivered by centrally presented patterns, interfered with response selection in the same way as laterally presented stimuli. Second, we asked whether such interference was equal for different kinds of stimuli. Participants were required to respond to the colour of two framed squares, two arrows, or two schematic eyes by pressing one of two lateralized response keys. The results consistently show that the Simon effect occurs independently of the nature of the stimulus, as classically reported for lateralized stimuli. Response times were influenced by the direction and frame-relative position of the stimuli, being faster for responses corresponding to the direction indicated by the stimuli than for noncorresponding responses regardless of stimulus types. Contrary to findings with lateralized nondirectional stimuli, such an effect increased with increasing RTs indicating that for centrally presented patterns the extraction of spatial information is time consuming.

Spatial location has been demonstrated to be automatically coded with a large variety of stimuli, even in situations in which it is irrelevant to the task to be performed (e.g., Tsal & Lavie, 1993). The effects of irrelevant spatial codes emerge very clearly in the Simon task in which participants are presented with two different lateralized patterns (i.e., placed in the periphery of the visual field) and are required to press the right-side key in response to one pattern, and the left-side key in response to the other (Simon & Rudell, 1967; see Hommel & Prinz, 1997; Lu & Proctor, 1995, for reviews). Even though participants are clearly instructed to select the response exclusively on the basis of the relevant nonspatial stimulus dimension, irrelevant information concerning stimulus location is processed. As a consequence, faster responses are made when the position of the stimulus and the position of the response key are located on the same side (right-right or left-left; i.e., corresponding S-R pairings) compared to when they are positioned differently (stimulus on the right side and response on the left side, or vice versa; i.e., noncorresponding S-R pairings).

Recent studies seem to suggest that stimulus position is not the only dimension capable of automatically activating a response spatial code that influences performance. For instance, central arrows have been shown to influence both voluntary (e.g., Posner, 1980) and automatic (e.g., Danziger, Kingston, & Ward, 2001; Eimer, 1997; Hommel, Pratt, Colzato, & Godijn, 2001; Ristic, Friesen, & Kingstone, 2002; Tipples, 2002) orienting of visual attention. Furthermore, it seems well established that centrally presented arrows (i.e., presented at central fixation) can produce the Simon effect (e.g., Masaki, Takasawa, & Yamazaki, 2000). This result is not surprising since arrows are commonly used to convey spatial information and have therefore acquired a directional meaning.

Gaze direction is another stimulus shown to deliver spatial information (e.g., Ansorge, 2003b; Zorzi, Mapelli, Rusconi, & Umiltà, 2003; Langton & Bruce, 2000). However, not only does it provide the observer with directional spatial information, but it can communicate different types of crucial information such as the focus of attention, interest, emotions, and intentions of others (e.g., Baron-Cohen & Cross, 1994; Emery, 2000). Eye direction is also capable of automatically and reflexively triggering the orienting behaviour of the observer (e.g., Driver et al., 1999; Friesen & Kingstone, 1998; Friesen, Ristic, & Kingstone, 2004; Langton & Bruce, 1999). All this makes gaze direction biologically relevant for survival and the eyes a key social cue for understanding the mind of others (Baron-Cohen, 1995).

Recently, Zorzi et al. (2003) showed that the direction of eye-like stimuli elicits a specific spatial code, independent from the stimulus spatial position, which can influence lateralized manual responses. …

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