Peter McLeod

From eye movements to actions: how batsmen hit the ball

In cricket, a batsman watches a fast bowlers ball come toward him at a high and unpredictable speed, bouncing off ground of uncertain hardness. Although he views the trajectory for little more than half a second, he can accurately judge where and when the ball will reach him. Batsmens eye movements monitor the moment when the ball is released, make a predictive saccade to the place where they expect it to hit the ground, wait for it to bounce, and follow its trajectory for 100–200 ms after the bounce. We show how information provided by these fixations may allow precise prediction of the balls timing and placement. Comparing players with different skill levels, we found that a short latency for the first saccade distinguished good from poor batsmen, and that a cricket players eye movement strategy contributes to his skill in the game.

Post-decision wagering objectively measures awareness

The lack of an accepted measure of awareness has made claims that accurate decisions can be made without awareness controversial. Here we introduce a new objective measure of awareness, post-decision wagering. We show that participants fail to maximize cash earnings by wagering high following correct decisions in blindsight, the Iowa gambling task and an artificial grammar task. This demonstrates, without the uncertainties associated with the conventional subjective measures of awareness (verbal reports and confidence ratings), that the participants were not aware that their decisions were correct. Post-decision wagering may be used to study the neural correlates of consciousness.

A dual task response modality effect: Support for multiprocessor models of attention

In Experiment I two groups of 11 men performed a continuous visual input/manual output task simultaneously with a two-choice tone identification task. One group responded vocally to the tones; one group responded with the hand not involved in the continuous tracking task. In either perceptual or stimulus uncertainty terms the two combinations were identical; the only difference between them was the modality of the two-choice responses. The continuous task was performed significantly worse when the two-choice responses were manual. The probability of response production on the continuous task was affected by the production of manual responses but not by the production of vocal responses. It was concluded that although the two manual responses were produced by a single limited capacity process, the manual and vocal responses were produced by independent processes. In Experiment II the same manual tracking task was combined with a mental arithmetic task at two levels of difficulty. Tracking performance was independent of the difficulty of the arithmetic task. These results support a multi-processor approach to attention as opposed to single channel models. Results of dual task studies which have used only one pair of response modalities are re-examined in the light of the response modality effect found in Experiment I.

Visual Reaction Time and High-Speed Ball Games

Laboratory measures of visual reaction time suggest that some aspects of high-speed ball games such as cricket are ‘impossible’ because there is insufficient time for the player to respond to unpredictable movements of the ball. Given the success with which some people perform these supposedly impossible acts, it has been assumed by some commentators that laboratory measures of reaction time are not applicable to skilled performers. An analysis of high-speed film of international cricketers batting on a specially prepared pitch which produced unpredictable movement of the ball is reported, and it is shown that, when batting, highly skilled professional cricketers show reaction times of around 200 ms, times similar to those found in traditional laboratory studies. Furthermore, professional cricketers take roughly as long as casual players to pick up ball flight information from film of bowlers. These two sets of results suggest that the dramatic contrast between the ability of skilled and unskilled sportsmen to act on the basis of visual information does not lie in differences in the speed of operation of the perceptual system. It lies in the organisation of the motor system that uses the output of the perceptual system.

Why good thoughts block better ones: The mechanism of the pernicious Einstellung (set) effect.

The Einstellung (set) effect occurs when the first idea that comes to mind, triggered by familiar features of a problem, prevents a better solution being found. It has been shown to affect both people facing novel problems and experts within their field of expertise. We show that it works by influencing mechanisms that determine what information is attended to. Having found one solution, expert chess players reported that they were looking for a better one. But their eye movements showed that they continued to look at features of the problem related to the solution they had already thought of. The mechanism which allows the first schema activated by familiar aspects of a problem to control the subsequent direction of attention may contribute to a wide range of biases both in everyday and expert thought - from confirmation bias in hypothesis testing to the tendency of scientists to ignore results that do not fit their favoured theories.

Do Fielders Know Where to Go to Catch the Ball or Only How to Get There

Skilled fielders were filmed as they ran backward or forward to catch balls projected toward them from a bowling machine 45 m away. They ran at a speed that kept the acceleration of the tangent of the angle of elevation of gaze to the ball at 0. This algorithm does not tell fielders where or when the ball will land, but it ensures that they run through the place where the ball drops to catch height at the precise moment that the ball arrives there. The algorithm leads to interception of the ball irrespective of the effect of wind resistance on the trajectory of the ball.

Filtering by movement in visual search

Search for a target defined by a conjunction of movement and form (e.g., an X moving up in a display of intermingled Os moving up and stationary Xs) is parallel. This result is also found if (a) the moving Os and target X move in unpredictable directions so that the moving stimuli do not form a clear perceptual group or (b) the nontarget Xs also move but in a known, different direction from the Os and target X. In contrast, search is slow and serial if the target may be unpredictably among either moving or stationary stimuli. These results suggest that a component of the visual system operates as a movement filter that can direct attention to stimuli with a common movement characteristic. The filtering cue can be moving (vs. stationary), or movement in 1 particular direction. The results do not support the view that attention can only be directed to groups defined by common fate.

Isolating cognitive modules with the dual-task paradigm: Are speech perception and production separate processes?

A dual-task paradigm is used to investigate whether the auditory input logogen is distinct from the articulatory output logogen. In the first two experiments it is shown that the task of detecting an unspecified name in an auditory input stream can be combined with reading aloud visually presented words with relatively little single- to dual-task decrement. The stimuli for both tasks are independent streams of random words presented at rapid rates. A series of control experiments suggest that the first task places a considerable information processing load on the auditory input logogen, the second a considerable load on the phonological output logogen, and that subjects do not switch between the two tasks. The fact that the two tasks can be combined with ease is therefore interpreted as supporting the view that the systems underlying reading aloud and listening are separate. The ease of performance when the input streams are in different modalities, compared to the difficulties when they are in the same, has implications for general models of attention.

Does probe RT measure central processing demand

Various authors have tried to assess the processing demands of a range of tasks by presenting a probe at different times during their performance. The assumption behind the technique is that the more processing capacity the main task requires the less will be left for processing the probe. Hence, it is claimed, the reaction time to the probe can be used to infer the capacity demands of the main task. An experiment is reported in which two groups of women combine manual responses to a visual Same/Different letter-match task with responding to an auditory probe. The only difference between the groups is that one responds manually to the probe and the other responds vocally. The two groups produce an entirely different pattern of interaction between the two tasks. Were there an absolute central demand of the letter-match task which could be measured by the probe technique this should appear irrespective of the form of the probe task. Since the pattern of probe RTs does depend on the form of the response to the probe it is concluded that it is not possible to use a single form of probe task as a neutral measure of the central capacity demand of the main task.

The Generalized Optic Acceleration Cancellation Theory of Catching.

The generalized optic acceleration cancellation (GOAC) theory of catching proposes that the path of a fielder running to catch a ball is determined by the attempt to satisfy 2 independent constraints. The 1st is to keep the angle of elevation of gaze to the ball increasing at a decreasing rate. The 2nd is to control the rate of horizontal rotation necessary to maintain fixation on the ball. Depending on the lateral velocity of the ball relative to the fielder, this rate may be zero or constant at a negative or positive value. The authors show that a simulated fielder implementing the GOAC strategy follows a path indistinguishable from that of real fielders running to catch balls thrown on the same trajectories.