Awareness and Confidence Ratings in Motion Discrimination

Abstract

We have extended our earlier investigations that demonstrated above chance direction discrimination of a moving single-dot target, presented within the blindfield of a hemianope (Weiskrantz et al, 1995 Proceedings of the National Academy of Sciences of the USA 92 6122 – 6126). Previous investigations pointed towards two distinct modes of processing, namely correctly discriminating the stimulus direction of motion when ‘aware’ or ‘unaware’ of its presentation. There have been arguments and counter arguments for the relationship between confidence and discrimination scores in normal observers [Kolb and Braun, 1995 Nature (London) 377 336 – 338; Morgan et al, 1997 Nature (London) 385 401 – 402].

We have investigated the relationship between correct direction-discrimination scores and both the awareness of a visual event and the confidence with which the discrimination is made as a function of the stimulus speed in a blindsight subject using binary and graded scales. Results show that the introduction of a six-point scale for the expressed level of awareness yielded similar results to those when the subject was given a binary choice to indicate the presence or absence of conscious awareness. Although the subject's confidence ratings in making a discrimination varied monotonically as a function of stimulus speed, the data obtained suggest that confidence and awareness, although related, are not functionally identical. The correct discrimination scores remained significantly above chance for a range of speeds even when the subject reported nonconfident. The correct discrimination scores were poorer but nevertheless well above chance for conditions where the subject was asked to report both confidence and awareness and improved if required to report only one of these parameters.