opposite effects

From Scholarpedia

Curator: Dr. Naotsugu Tsuchiya, California Institute of Technology, Pasadena, CA, USA
Curator: Dr. Christof Koch, Division of Biology, Caltech, Pasadena, CA

Can top-down attention be opposed to consciousness?

Attention enhances neuronal processing, yet, it sometimes impairs performance of the task

Attention and its neuronal correlate can be understood in the context of selection and biased competition (Desimone and Duncan, 1995): attention acts as a winner-take-all, enhancing one coalition of neurons (representing the attended object) at the expenses of others (non-attended stimuli) (Lee et al., 1999). Paradoxically though, reducing attention can enhance awareness (Olivers and Nieuwenhuis, 2005) and certain behaviors (Reber, 1976; Wong and Weisstein, 1983; Yeshurun and Carrasco, 1998; Beilock et al., 2002).

In the Rubin’s ambiguous face/vase figure (see Attention and Consciousness/How to manipulate and measure visual consciousness), the percept switches between two faces seen in profile and a vase. Discrimination of high-frequency stimuli, such as a line, presented on the face area when it is perceived as the figure is better than when it is perceived as the ground. If a blurred, low spatial frequency stimulus is presented in this region, it is better discriminated when the face is perceived as the ground. Something similar occurs when the target stimulus is presented on the vase area. In other words, a low spatial frequency stimulus is better detected on the unattended ground (Wong and Weisstein, 1982, 1983). Likewise, Yeshurun and Carrasco (Yeshurun and Carrasco, 1998) showed that attention impairs the performance of texture segregation when the subject is required to process low spatial frequency information.

Opposing effects of attention and consciousness

Note that a complete orthogonal manipulation of attention and consciousness has not been performed in any of the following these examples.

Figure 1: When an adaptor is attended, the associated afterimage becomes weaker and appears later (blue gradation (Lou, 2001; Suzuki and Grabowecky, 2003; Wede and Francis, 2007)). Yet paradoxically, when the adaptor is rendered invisible, its afterimage is substantially weakened (pink gradation (Gilroy and Blake, 2005; Tsuchiya and Koch, 2005)).

Attention weakens afterimages, visibility enhances afteriamges

Consider the formation of afterimages (Fig.1). If an item is attended during adaptation, the intensity of the subsequent afterimage becomes weaker and its duration shorter compared to an unattended item(Lou, 2001; Suzuki and Grabowecky, 2003; Wede and Francis, 2007). If, however, the image is suppressed during adaptation, the afterimage is substantially weakened (Gilroy and Blake, 2005; Tsuchiya and Koch, 2005). Thus, focal attention and consciousness have opposing effects (Tsuchiya, 2006).

Speed of perceptual switches is modulated by attention and visibility of bistable stimuli

Figure 2: When attention is withdrawn from a visible bistable/rivalry target (here, a Necker cube), the rate of perceptual flips slows down (blue gradation (Paffen et al., 2006; Pastukhov and Braun, 2007)). When the target stimulus is intermittently presented (stabilization), the opposite may occur; withdrawing attention from the target causes less stabilization, that is, perceptual flips speed up (pink gradation (Kanai and Verstraten, 2006)).

Next, consider freezing in bistable perception (Fig.2) (Orbach et al., 1963; Leopold et al., 2002). During continuous viewing of an ambiguous stimulus, the percept flips stochastically. Yet if the bistable figure is briefly removed (leaving the display empty), the dominant percept at the start of the new display is the same as the one when the percept disappeared. This freezing is disrupted if spatial attention is distracted from the empty display(Kanai and Verstraten, 2006), most likely by disrupting memory buildup. This can be thought of as speeding up perceptual switching. Yet distracting focal attention during bistable perception slows down the switching rate (Paffen et al., 2006; Pastukhov and Braun, 2007). In other words, withdrawing focal attention when the stimulus is invisible, not consciously seen, disrupts perceptual freezing, while withdrawing attention when the stimulus is visible slows down switching.

Opposing effects of attention and consciousness in decision making

Figure 3: When confronted with a complex decision where many items must be remembered (i.e., the list is invisible), distracting subjects from the decision making process improves performance (pink gradation (Dijksterhuis et al., 2006)). The last figure is modified from (Dijksterhuis et al., 2006). From (Koch and Tsuchiya, 2007) with permission.

Finally, consider complex decision-making (Fig.3). The Dijksterhuis’ (Dijksterhuis et al., 2006) study consisted of three phases: examination of items, deliberation, and decision. One of either 4 or 12 properties for each of 4 cars was shown one at a time during the examination phase. Subjects then deliberated for several minutes without the attributes being visible (that is, subjects had to remember them; this can be thought of as an ‘invisible’ condition) before making a purchasing decision. Dijksterhuis and colleagues manipulated whether or not subjects were cognitively engaged during the deliberation period. They concluded that when faced with working memory overload, an explicit strategy based on deliberate and rational thought leads to poor decision making for a complex decision, while distracting subjects when they decide which car to buy greatly increased the probability of a correct choice. We surmise that if the list of items would have been present throughout the decision-making period – thereby reducing working memory load – an attentional distracting task would degrade purchasing performance. For a related finding in implicit learning, see (Reber, 1976).

References

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