Unconscious Cueing via the Superior Colliculi: Evidence from Searching for Onset and Color Targets.

Brain Sci. 2012, 2, 33-60; doi:10.3390/brainsci2010033 OPEN ACCESS brain sciences ISSN 2076-3425 www.mdpi.com/journal/brainsci/ Article Unconscious Cueing via the Superior Colliculi: Evidence from Searching for Onset and Color Targets Isabella Fuchs 1 and Ulrich Ansorge 1,2,* 1 2 Faculty of Psychology, University of Vienna, Liebiggasse 5, 1010 Vienna, Austria; E-Mail: Institute of Cognitive Science, University of Osnabrück, 49069 Osnabrück, Germany * Author to whom correspondence should be addressed; E-Mail: ; Tel.: +43-1-4277-47823; Fax: +43-1-4277-47819. Received: 13 December 2011; in revised form: 3 February 2012 / Accepted: 7 February 2012 / Published: 15 February 2012 Abstract: According to the bottom-up theory of attention, unconscious abrupt onsets are highly salient and capture attention via the Superior Colliculi (SC). Crucially, abrupt onsets increase the perceived contrast. In line with the SC hypothesis, unconscious abrupt-onset cues capture attention regardless of the cue color when participants search for abrupt-onset targets (Experiment 1). Also, stronger cueing effects occur for higher than lower contrast cues (Experiment 2) and for temporally, rather than nasally, presented stimuli (Experiment 3). However, in line with the known color-insensitivity of the SC, the SC pathway is shunted and unconscious abrupt-onset cues no longer capture attention when the participants have to search for color-defined targets (Experiment 4) or color-singleton targets (Experiment 5). When using color change cues instead of abrupt-onset cues, the cueing effect also vanishes (Experiment 6). Together the results support the assumption that unconscious cues can capture attention in different ways, depending on the exact task of the participants, but that one way is attentional capture via the SC. The present findings also offer a reconciliation of conflicting results in the domain of unconscious attention. Keywords: vision; attention; color; subliminal Brain Sci. 2012, 2 34 1. Introduction At any instance in time, our visual world provides a vast amount of visual input. Since human mental capacity is limited, only a fraction of the available information is selected for purposes such as perception, memory and action control, while the rest of the information is ignored. In the visual modality, this selectivity is called selective visual attention [1]. One important issue concerns the role of selective visual attention in the division of labor between unconscious (or subliminal) visual processing on the one hand and conscious vision on the other. A related important question is how this division of labor is implemented in the human brain’s visual system. One hypothesis about the relationship between conscious and unconscious vision is that selective visuo-spatial attention (i.e., the selection of positions or areas in the visual field) is a necessary (though not sufficient [2]) prerequisite for at least some forms of conscious visual perception [3,4], but see [5]. For example, according to feature-integration theory, selective visuo-spatial attention is necessary for the binding of different visual features (e.g., red color and round shape) into one perceived object (e.g., a tomato) [6]. Crucially, if it is true that attention serves conscious visual perception, it follows that attention should (at least partly) operate before conscious vision—that is, visuo-spatial attention should operate on the basis of subliminal visual information, too [3]. This has been demonstrated in cueing experiments with abrupt-onset singleton cues [7,8]. In cueing experiments, participants have to search for targets, and in each trial, one target is shown at one out of several positions [9,10]. The participants have to find this target, discriminate it, and respond to it. When presenting a single abrupt-onset briefly before the target with a Stimulus Onset Asynchrony (SOA) of up to 200–300 ms at the same position (SP) as the target, locating the target is facilitated. This facilitation is reflected in faster responses to targets in SP conditions than to targets at a different position (DP) than the cue. This facilitative cueing effect presumably reflects the capture of attention by the cue [11]. As explained, target perception requires that attention is shifted towards target locations [3,6]. Since the cue captures attention towards its location, in SP conditions attention is already at the target position. In contrast, in DP conditions attention has to be directed away from the cue to the target position, which can only be performed after target onset. This capture effect (i.e., an SP-DP performance difference) is found with single abrupt-onset cues that are not predictive for the most likely target position [9,10] and it turns into Inhibition Of Return (IOR)—that is, slower responses for SP than DP targets—with SOAs beyond 300 ms [12–14]. IOR could be due to a sequence of capture by the cue, subsequent deallocation of attention away from the cue during the longer SOA, and a reluctance to reorient to the cued position if the target is finally presented there [13,15]. IOR might also reflect motor inhibition [14] or result from perceptual adaptation [12]. Whatever the exact origin of IOR, in line with subliminal attention, both the facilitative cueing effect with the short SOA and IOR with longer SOAs have also been found with subliminal abrupt-onset cues that were not seen by the participants (i.e., could not be reported with better than chance accuracy) [7,8,15,16]. For example, presenting one disk as a single abrupt-onset cue on the left or on the right of a computer screen with a head start of 16 ms before two additional disks (at screen center and on the opposite screen side), this abrupt-onset cue can barely be seen: Due to the short onset difference, the participants were unable to decide whether a cue was presented on the left or on the right during a cue-discrimination task at the end of the experiment [15]. These subliminal cues Brain Sci. 2012, 2 35 captured attention [15,17]: Target detection was facilitated with a short cue-target SOA of 16 ms in SP conditions compared to DP conditions. In addition, with a longer SOA of 1,016 ms the subliminal cue led to IOR [15,17]. Exactly how the brain’s visual system brings about subliminal vision in general and subliminal attention in particular, however, is currently debated. One party of researchers thinks that at least some forms of unconscious vision reflect processing along the visual system’s parvocellular projection, leading from the retina to the cortex, via the Lateral Geniculate Nucleus (LGN) of the thalamus [18], and many forms of unconscious visual processing are probably of cortical origin [19,20]. However, another party of researchers recently proposed that subliminal attention at least partly reflects contrast-elicited attentional capture mediated by midbrain structures, namely neurons in the Superior Colliculi (SC) [1 (...truncated)