Detection and identification of words and letters in simulated visual search of word lists

On determining what is unconscious and what is perception

In sum, dichotic listening tasks are appropriate for testing whether perception requires attention. The separate issue of the possible presence of perception that can never be brought under the spotlight of awareness should indeed be investigated by paradigms such as masking. However, the ultimate criterion for availability to awareness must be phenomenal experience. The discrepancy between thresholds of different perceptual indices is an important empirical finding, but its theoretical interpretation is not straightforward. In addition, it is suggested that we worry about the possibility that so-called indirect evidence reflects side effects of perceptual processing rather than the contents of its final product. In that case, what are being observed are vestiges of the processing of stimuli that do not make it to awareness. Whether those stimuli are below the threshold for overt response is an open question.

Semantic activation without conscious identification in dichotic listening, parafoveal vision, and visual masking: A survey and appraisal

When the stored representation of the meaning of a stimulus is accessed through the processing of a sensory input it is maintained in an activated state for a certain amount of time that allows for further processing. This semantic activation is generally accompanied by conscious identification, which can be demonstrated by the ability of a person to perform discriminations on the basis of the meaning of the stimulus. The idea that a sensory input can give rise to semantic activation without concomitant conscious identification was the central thesis of the controversial research in subliminal perception. Recently, new claims for the existence of such phenomena have arisen from studies in dichotic listening, parafoveal vision, and visual pattern masking. Because of the fundamental role played by these types of experiments in cognitive psychology, the new assertions have raised widespread interest.

The purpose of this paper is to show that this enthusiasm may be premature. Analysis of the three new lines of evidence for semantic activation without conscious identification leads to the following conclusions. (1) Dichotic listening cannot provide the conditions needed to demonstrate the phenomenon. These conditions are better fulfilled in parafoveal vision and are realized ideally in pattern masking. (2) Evidence for the phenomenon is very scanty for parafoveal vision, but several tentative demonstrations have been reported for pattern masking. It can be shown, however, that none of these studies has included the requisite controls to ensure that semantic activation was not accompanied by conscious identification of the stimulus at the time of presentation. (3) On the basis of current evidence it is most likely that these stimuli were indeed consciously identified.

Combining attributes in rapid serial visual presentation tasks

A series of three exploratory experiments sought to compare and contrast two broad classes of theory pertaining to visual information pick-up. One theoretical approach, exemplified by Keele and Neill (1978) and by Treisman (1977) emphasizes the relatively passive, parallel development of information codes, with subsequent attentional integration of contiguous codes into a percept. Another theoretical approach, exemplified by Broadbent (1977a) emphasizes the relatively active, sequential, recursive interrogation of a visual display in which the pick-up of each piece of information guides the perceptual system in its quest for more information. The manner in which separable attributes of visual information are picked up and combined was studied by manipulating the roles of different attributes in a rapid serial visual presentation (RSVP) paradigm. Observers were asked to report the name of a letter in a specified target colour; to report the colour of a specified target letter; to report the colour of a specified target numeral embedded in a list of letters; to report the colour of an unspecified numeral embedded in a list of letters; and to perform the latter two tasks without knowing in which of two alternating spatial positions the target might appear. Examination of the patterns of mis-combinations of attributes from target and non-target stimuli yields evidence both for and against each theoretical position, and suggests that the two might better be considered as modes of processing available to the perceptual system, rather than as intrinsic properties of that system.