On the information-based regulation of movement: What Wann (1996) may want to consider.

Abstract

On the basis of a critical review of studies that examined the use of temporal information in the regulation of movement, J. P. Wann (1996) concluded that there is little evidence in favor of the use of tau. Although more experimental work is certainly needed, progress can only be made if (a) the conceptual confusion emanating from a lack of distinction between specification (i.e., information) and what is specified (i.e., relevant property of the environmentactor system) is resolved, and (b) the way in which information is used in the regulation of movement is reconsidered. It is argued that continuous control models incorporating firstorder time-to-contact related information not only explain the results obtained but also allow testable accounts of the principles involved in kinematic trajectory formation.A change in the relative distance between an observer and an object (or a surface) gives rise to a change in the optic angle subtended at the point of observation by the object. Thus, a change in the optic angle may be used by an observer to detect the existence of relative motion. Moreover, the pattern of change of the optic angle contains information about certain characteristics of the relative motion, signaling, for instance, whether the relative distance increases or decreases and, in the latter case, whether a collision is imminent (Schiff, 1965). Lee (1974Lee ( ,1976Lee ( ,1980 demonstrated that besides these qualitative aspects, the pattern of change of the optic angle also contains quantitative temporal information, signaling the time remaining until contact if the velocity of approach were to remain constant.The identification of such quantitative temporal information in the optic flow pattern opened the door for the development of a theory of the (temporal) regulation of movement, and since then a large number of studies have been reported that attempted to test and/or further develop such a theory. Today, the optical flow pattern descriptor identified by Lee (1974Lee ( , 1976Lee ( , 1980)-which he coined T (tau)-figures prominently in most textbooks on perception or movement. However, this by no means implies that the debate on the manner in which, if at all, such an optical variable is used in the regulation of movement is closed, as is exemplified by the critical article of Wann (1996). On Distinguishing Specification FromWhat Is SpecifiedBefore entering into the argument about the use of T-like variables in the timing of action, a persistent and pervasive conceptual confusion needs to be resolved first. This confusion is generated by the fact that, more often than not, students of perception and movement fail to distinguish between the property of the Environment-Actor System (EAS) that is thought to be relevant for the regulation of movement and its optical (or acoustical, mechanical, chemical, etc.) representation, that is, the distinction between what is specified (the property of the EAS) and its specification (the informative flow pattern that can be detected). In the introductory example...

Time-to-Contact Estimation of Accelerated Stimuli Is Based on First-Order Information.

“…Even though this hypothesis has been much disputed in recent studies of the control of interceptive actions (e.g., Bootsma et al, 1997;Dessing, Bullock, Peper, & Beek, 2002;Lee et al, 1983;Montagne et al, 2001;Peper, Bootsma, Mestre, & Bakker, 1994;Savelsbergh et al, 1991), it must be the case that the specific characteristics of this task require a prediction, as control of the action is not possible after releasing the ball.…”

“…They showed that the angle-time functions of the three different height conditions lie much closer to the TTC1-time function than to the TTC-time function. 2 Generalizing the TTC1 hypothesis to nonradial approaches, Bootsma and colleagues (Bootsma et al, 1997;Bootsma & Oudejans, 1993) proposed that TTC is specified by information combining the relative velocity of the expansion of the optical contour of a moving object (˙) with the relative velocity of the contraction of the visual angle between the object and the point of interception (˙). This information variable, ( , ), specifying TTC1(x) at any point in space, is formalized by 1/ ( , ) ϭ ˙/sin Ϫ ˙/ sin ϭ Ϫ1/TTC1(x), where ˙is the inverse of ( ) as defined by Lee (1976) when is small (when Յ 10°, sin Ϸ ), corresponds to the angle formed at the participant's observation point by the object and the point of interception, and ˙c orresponds to the variation of this angle as a function of time (see Figure 2).…”

Getting hold of approaching objects: In search of a common control of hand-closure initiation in catching and grasping

“…1 Following Bootsma, Fayt, Zaal, and Laurent (1997), we distinguish the optical time-to-contact information (τ) from the organism-environment property that it specifies, TC 1 (D). TC 1 (D) is defined as the first-order time-to-contact, the time that distance gap D will be closed when closing velocity would remain constant.…”

Modelling the control of interceptive actions

“…Recently, we (Dessing et al 2002) further analysed the generic RV control structure inherent in two prospective controllers of hand movements in catching, both based on RV control, namely Peper et al's (1994) model and an alternative version of this model formulated by Bootsma et al (1997). On the basis of a comparison with the experimental data reported in Montagne et al (1999Montagne et al ( , 2000, it turned out that both models predicted overshoots of the future interception point in some conditions where no overshoots occurred in the data.…”