Jack, Anthony Ian; (1999) Perceptual awareness in visual masking. Doctoral thesis (Ph.D), UCL (University College London).

Text out.pdf Download (13MB)

Abstract

The hypothesis of perception without awareness has been a controversial topic in experimental psychology ever since Ericksen's (1960) influential critique. This thesis examines the philosophical claim, famously made by Nagel (1974), that consciousness marks a distinction between phenomena which can be described by science (i.e. physical phenomena), and those which cannot (i.e. mental phenomena); and reviews the methodological debate concerning the measurement of awareness. It is argued that subjective, or phenomenological, evidence is necessary for the development of a theoretical account of perceptual awareness; and that, contrary to the arguments of researchers such as Merikle (1984), this evidence can be incorporated into a scientific methodology. A new approach for the investigation of perceptual awareness is proposed which equates conscious identification with the operation of one of a set of higher-order cognitive processes. This set includes, amongst other processes, the encoding of information into episodic memory and the process of exclusion which occurs in the Jacoby Exclusion task (Debner & Jacoby, 1994). A series of eleven experiments, involving the visual presentation of pattern masked stimuli, investigates the evidence for perception without awareness. The results are interpreted as supporting the hypothesis of perception without awareness, and indicate that the processes underlying discrimination differ from those underlying conscious identification. However more importantly, the experimental evidence is seen to inform an information processing model of conscious and unconscious processing (Norman & Shallice, 1980). Finally, results from four of the experiments reported (and two further experiments reported in appendices) provide evidence of qualitatively different processing of stimuli masked at 17ms stimulus-mask onset asynchrony (SOA), as compared with stimuli masked at 33ms or longer SOA. This finding may be pertinent to Crick & Koch's (1990) 'temporal tagging' hypothesis, which relates 40Hz oscillations observed in visual cortex to attentional selection.

Download activity - last month

Export as JSONCSVXML

Download activity - last 12 months

Export as JSONXMLCSV

Downloads by country - last 12 months

Export as CSVXMLJSON

Archive Staff Only

View Item