The Motion Aftereffect: A Modern Perspective, edited by George Mather, Frans Verstraten and Stuart Anstis

MIT Press, 1998. £16.95 (xii + 220 pages)ISBN 0 262 13343 1A former student of mine had a filthy habit. He was enslaved by a television channel whose main attraction was a moving ‘tape’ of financial-market quotations. One day, this student reported breathlessly a great discovery: after watching the moving tape, various objects, including his can of high-caffeine soda, appeared to move. I was so pleased by his keen eye that I hated telling him that Lucretius, Purkinje and numerous others had beaten him to this illusion. In fact, over the centuries, many people have discovered or re-discovered this phenomenon, called the motion aftereffect (MAE), waterfall illusion, snowfall aftereffect or, in honour of my student, the stock-market illusion.Now, two millennia after MAE was initially reported, we have The Motion Aftereffect; the first book devoted entirely to my student’s discovery. And what an enthusiastic effort it is. The book’s introduction informs readers that ‘The MAE has thus been at the heart of modern neuroscience since its inception.’ Many readers of TINS will be puzzled, at least, by this assertion about the proximity of MAE to the heart of neuroscience. The hyperbole in the introduction is echoed in the book’s epilogue: ‘The MAE presents perhaps the clearest example in modern neuroscience of the link between neural events and perceptual experience.’ Such exuberance is refreshing, but few researchers would count MAE among the genuine successes in the struggle to connect perceptual experience to neural events. Despite recent successes in applying functional neuroimaging to MAE (Ref. 1xHe, S., Cohen, E.R., and Hu, X. Curr. Biol. 1998; 8: 1215–1218Abstract | Full Text | Full Text PDF | PubMedSee all ReferencesRef. 1), we are still far from understanding the neural events that generate it. In fact, contributors to this book, such as Michael Niedeggen and Eugene Wist, are very clear about the difficulties of identifying the neural events and changes that accompany prolonged viewing of motion.Nicholas Wade and Frans Verstraten open the book with an excellent, intelligently selective history of work on MAE. The chapter is unusual in acknowledging contemporary MAE research’s 90-year-old debt to Adolf Wohlgemuth’s one and only publication on vision. Excluding self-citations, Wohlgemuth is the second most frequently cited author in this book (top honours belong rightly to Horace Barlow). The numerous experiments reported in Wohlgemuth’s monograph2xWohlgemuth, A. Br. J. Psychol. 1911; 1: S1–S117See all References2 constitute a superb starting point for aspiring students of MAE. This is true even when Wohlgemuth was completely wrong, as he was when he claimed that MAE was uninfluenced by attention. The excellent chapter by Jody Culham, Shin’ya Nishida and others, rights the record on the dependence of MAE on attention. It also introduces the miscellany of MAEs that can be produced by stimuli that comprise multiple directions of motion, for example, moving plaids.Various chapters in The Motion Aftereffect (notably those by Peter Thompson, and by Bernard Moulden and associates) confirm that great progress has been made towards understanding the numerous stimulus determinants of MAE. Recent revelations include the idea that prolonged exposure to visual motion – drifting random dots, a waterfall, a financial market tape – produces not one MAE but several, which probably involve several different regions of the brain. These MAEs differ in degree of binocularity, spatial tuning and various temporal characteristics.Because MAE can be measured so easily – an investment in a stopwatch suffices for a bare-bones operation – it is easy to overlook the subtleties of making proper measurements. But researchers in any field must understand their measuring instruments and how those instruments might colour the phenomena being measured. In his chapter, Allan Pantle defines and clarifies issues that are raised by the existence of alternative methods of measuring MAE. Pantle argues convincingly that measures of MAE tend to be reactive, that is, the measurements change the system being measured. In that same chapter, we are reminded that MAE (the appearance of phenomenal, illusory motion) is not the only consequence of prolonged exposure to motion. Such exposure also produces direction-selective threshold elevation, changes in sub-threshold summation, as well as changes in perceived direction and in apparent speed. Although they are not measured as easily as MAE, some of these non-MAE sequelae of visual motion can be captured with less contamination from reactivity.Practitioners of psychophysics have long endorsed the slogan, which is repeated approvingly in this book, that ‘aftereffects are the psychologist’s microelectrode.’ Of course for many psychologists their microelectrode is the real thing, a microelectrode, not a low-price substitute. Nevertheless, before we think about replacing microelectrodes with aftereffects it is important to remember how blunt these blunt instruments really are. Unaided by functional neuroimaging, MAE studies yield only the crudest localization of the site (or sites) at which the phenomenon is generated. With the MAE as our electrode, we have essentially no idea where we are recording from.There is no doubt that the MAE is a striking phenomenon; it never fails to intrigue and elicit exclamations of ‘Oh, wow!’ Interest in MAE (and in visual motion more generally) has grown considerably in recent decades, which enhances the timeliness of this book. However, it is not clear that MAE can ever be a major source of insight into the operation of the nervous system. This concern aside, The Motion Aftereffect is certainly a very good place to go for a brief, thoughtful introduction to the aftereffects of visual motion.