Inattentional Blindness: by Arien Mack and Irvine Rock

Contemporary psychologists more and more tend to seek explanations not within psychology, but outside of it, in neighboring disciplines that at the moment are enjoying greater prestige. It is as if they do not consider mental facts to be real. All too often this tendency results in a failure to advance our knowledge of the psychological problem under investigation.Irvin Rock, 1972Visual search and visual attention have been a consistently popular topic for at least 15 years. Possible reasons for this interest are many. First, it afforded a quantitative approach to study suprathreshold vision in ways relevant to real life situations such as finding ones car in a parking lot. For cluttered displays, adding more distractors added proportionately greater time to do the search. For simpler displays, where targets appeared to ‘popout,’ there was no dependence of reaction time on distractor number. Most important were new theories of visual attention1xPreattentive processing in vision. Treisman, A. Comp. Vis. Graph. and Image Proc. 1985; 31: 156–177Crossref | Scopus (482)See all References, 2xToward an axiomatic theory of preattentive vision. Julesz, B. See all References which considered the above findings to constitute a natural dichotomy and postulated primitives or ‘features’ of early vision (akin to the receptive field properties single visual neurons) as a way to explain it. Broadly speaking, they asserted that: (1) visual search would be parallel and preattentive if the elements were matched to the early analyzers of the visual system; (2) visual search would be serial and attentive if targets and distractors were complex and not distinguishable by early primitive mechanisms themselves. It was assumed that attention was not required for ‘parallel, preattentive search’ and whether or not a target popped out was determined by the properties of primitive analyzers. Such ideas were quickly and widely adopted by a generation who had come of age after the spectacular discoveries of single unit visual neurophysiology of the 50s and 60s, seeming to furnish a plausible fit between the best of what neurophysiology had to offer and at least some aspects of everyday visual perception. Against this accepted understanding, Mack and Rock have written a purely psychological account in the form of an experimental monograph, one that is likely to become a landmark because it challenges, and I believe eventually overturns, these seemingly well established ideas.They begin by questioning whether it is reasonable to conclude that no attention was required for visual search experiments, particularly if the task of the observer is to attend to the array and to intend to see it. As a result of this query, a truly novel method was conceived, correcting a flaw common to the class of experiments designed to evaluate the necessity of attention for visual perception. Such studies usually ask an observer to report a visual event under normal conditions, comparing it to conditions where an arduous diverting task is present. In the dual task condition, the observer knows that he must do both tasks and there is always the likelihood that despite the difficulty of a diverting task, a small amount of attention will be allocated to the other task.To achieve maximum inattention in relation to a specific visual stimulus, Mack and Rock presented a diverting task alone with no mention of any other stimulus or task, repeating this for 3–4 trials. Embedded in the next trial along with the diverting stimulus was the stimulus of interest, unannounced and therefore unexpected which the subject was also queried about. It should be noted that this is a most unusual experiment because subjects can only be tested once, for just one trial. After being asked once about an unexpected stimulus, subjects can no longer be assumed to be naively inattentive. This means that an unusually large number of fresh subjects were required. Undaunted by the necessity of thousands of subjects, Mack and Rock were amply rewarded.First they found that in dozens of experiments, an average of 25% of the subjects completely missed otherwise evident stimuli. So dramatic and so consistent were these results that the authors dubbed the phenomenon ‘inattentional blindness’ (IB). In addition, so called preattentive processes, such as grouping by similarity, proximity, etc. were all severely degraded by conditions of inattention. Interestingly, IB could be much stronger at the fovea, such that as many as 80% of the subjects missed targets here if the diverting stimulus was presented to the parafovea. These findings argue against the notion of preattentive perception and its hypothesized basis in early cortical physiology, advancing the view that without visual attention, there is no conscious visual perception.3xAttentional requirements in a ‘preattentive’ feature search task. Joseph, J.S., Chun, M.M., and Nakayama, K. Nature. 1997; 387: 805–807Crossref | PubMedSee all References, 4xAttention, pattern recognition and popout in visual search. Nakayama, K. and Joseph, J.S. : 279–298See all ReferencesGiven the title, this might seem to be the main point of the book, but it doesn’t end here. Later experiments indicate that meaningful stimuli, such as ones own name, or a happy face, were able to break through inattentional blindness, suggesting perhaps that the selectivity of attention is determined late, that the relatively high level meaning of the stimulus governs whether we will become aware of it.5xAttention: some theoretical considerations. Deutsch, J.A. and Deutsch, D. Psychol. Rev. 1963; 70: 80–90Crossref | PubMed | Scopus (388)See all References This indicates that inattentional blindness is not the early interruption of input but a limitation of its later distribution, analogous in part to parietal neglect. Their study of semantic priming without awareness under conditions of IB confirm this view. Thus, rather than limiting the transmission of a visual input, perhaps attention allows it to be distributed more widely in the brain and as a conscious percept.6xA Cognitive Theory of Consciousness. Baars, B.J. See all References In sum, and in contrast to earlier physiologically inspired models of visual attention, this book whets our appetite for a new, richer, and fuller understanding of perception and its relation to conscious and unconscious mental processing.Sadly, Irv Rock has not lived to see this book completed. Yet, it is fitting that Mack and Rock have bucked the tide he derided a quarter century earlier and we are all the better for it.