Monitoring CCTV and watching football: expert-novice differences in the magnitude of a visuo-motor buffer

The presence of a visuo-motor buffer of around half a second to a second has been proposed to account for performance in real-world tasks such as motor racing (Land & Tatler, 2001), hitting the ball in cricket (Land & MacLeod, 2000), making tea (Land, Mennie & Rusted, 1999) and sandwiches (Hayhoe, 2000). In addition, the magnitude of this buffer appears to be constant across experts and novices (e.g. Land and Furneaux, 1997). To examine this issue, we investigated performance on two very different tasks, but using similar methods: monitoring closed-circuit television (E1) and monitoring a football (soccer) match (E2). We tracked eye movements in both tasks. Observers viewed either real CCTV footage from an urban environment, or a videotaped 5-a-side football match. A joystick was used to continuously indicate either the degree of perceived suspiciousness (E1) or the probability of an imminent goal (E2). We performed correlations between manual responses and the between-subjects variability in eye position (i.e. the degree of spread of fixations at each time). To calculate buffer magnitude, we repeated this at all possible temporal lags between these two measures and searched for the maximal negative correlation coefficient. In both experiments, and particularly for CCTV monitoring, we observed a greater lag for trained than untrained observers. Undergraduate observers' performance was consistent with previous findings of a buffer of around half a second, but trained CCTV operators' responses occurred, on average, over two seconds after eye positions started to converge. This cannot be explained purely from previous lag estimates and is suggestive of differences in processing between experts and novices in these tasks.