This chapter presents findings indicating that psilocybin-induced visual distortions and impaired executive functioning originate in temporary disruptions of attentional mechanisms. It then revisits a predictive processing account of neural processing and argues that this lacks the resources to provide a unified model of the perceptual mechanisms underpinning psychedelic experiences caused by classic hallucinogens such as psilocybin, lysergic acid diethylamide (LSD), and mescaline. Lastly, an alternative theory of perceptual processing is proposed—the Gist Theory of Perception—that can better explain how the psilocybin-induced (...) disruptions of attentional mechanisms may elicit psychedelic experiences. (shrink)

Fazekas and Overgaard () present a novel, multidimensional model that explains different ways in which conscious representations can be degraded. Moreover, the authors discuss possible mechanisms that underlie different kinds of degradation, primarily those related to attentional processing. In this letter, we argue that the proposed mechanisms are not sufficient. We propose that attentional mechanisms work differently at various processing stages; and factors that are independent of attentional ones, such as expectation, previous experience, and context, should be accounted for if (...) we are aiming to construct a comprehensive model of conscious visual perception. (shrink)

In The Principles of Psychology, William James (1981) has long ago suggested that attending to a stimulus can make it appear more ‘vivid and clear.’ Pre-cueing, the procedure in which a cue stimulus is presented to direct a subject’s attention to the location of a test stimulus, has been used to test James’ hypothesis (Posner, 1978; Carrasco et al., 2004; Carrasco, Loula, & Ho, 2006; Yeshurun & Rashal, 2010; Carrasco, 2011). One recent debate concerns whether the effects of pre-cueing and (...) other perceptual changes associated with covert attention are evidence for cognitive penetration. In this paper, we argue that the pre-cueing effects associated with covert attention are similar to perceptual learning effects, despite the former having more transient effects than the latter. -/- . (shrink)

Philosophical accounts of visual perception have long had to contend with questions of perceptual relativity: visual phenomenology seems to be influenced by factors independent of the objective properties of the external objects we perceive. More recently, a host of such examples has emerged from psychological studies on visual attention. In two prominent accounts of the consequences of this research, Block argues that these effects occur without changes in the way one visually represents the world to be. If true, this would (...) undermine representationalist accounts of the phenomenology of perception, which share a commitment to the claim that phenomenal character supervenes on representational content. Block’s thesis is based on experiments involving non-selective attention, and he draws the metaphysical conclusion that the resources representationalists need to distinguish veridical from illusory perception are nonexistent. The empirical evidence he considers is highly compelling, as is the ‘landscape’ model of attention that appears to underwrite it. However, in discussing these issues, Block also considers a representative example of selective attention, wherein he concedes a point that provides grounds for a plausible representationalist response. I assemble and assess this response, revealing the contradiction at the heart of Block’s thesis, and conclude, that the representationalist should remain unmoved. (shrink)