Is The Visual World a Grand Illusion ?

This excellent and absorbing collection – a special issue of the Journal of Consciousness Studies, edited by Alva Noë, now published in separate book form – comprises fourteen papers dealing with responses to certain very striking recent discoveries about the limitations of visual attention. A cluster of experiments on “Change Blindness”, “Inattentional Blindness” and associated phenomena appear to demonstrate extremely counter intuitive results. According to one plausible characterisation, these results show that we consciously take in far less of the visual world than it seems we are aware of. It is worth briefly summarising the results of two recent sets of experiments, in order to give a flavour of this work. In ‘Gorillas in our Midst’ (Simons, D. and Chabris, C., Perception, 1999, 28), subjects were asked to perform a task that involved watching a video of a casual basketball game that lasts for about a minute. The task involves counting the number of consecutive passes between members of the one of the teams. While the basketball is being thrown from player to player, something unexpected takes place: a person dressed in a black gorilla-suit walks through the play, stops briefly in the centre of the picture, thumps his chest, and then walks off. Although most subjects correctly record the number of passes made by the team, at least half of these subjects fail to notice the gorillasuited interloper, who is visible for about nine seconds. When shown the video sequence a second time they are amazed to observe what they had previously overlooked. In Change Blindness experiments, a picture is displayed of a couple in the foreground with a number of buildings in the background. A brief flicker interrupts the display, which then returns with one substantial change – a large building in the background is no longer visible. This display remains visible for a second or so, and then again the flicker occurs and the switch is made, returning to the original picture. It may take many such alternations between images before the subject finally notices the large scene change not previously attended to; again, this produces surprise on the part of the subjects, when they realise they have overlooked an apparently obvious change. What is agreed by all theorists is that the phenomena of Change and Inattentional Blindness, etc, are well established. These experiments provide strong evidence about the limits of attention. What is less