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angle (resolution, 0.0440), a strain gauge torque transducer to measure torque (0.01 N accuracy), bearings to allow the wheel to rotate freely (isotonic control), and a clamp to lock the column in position (isometric control). 3 EXPERIMENTS

Three experiments were performed to investigate the response of the driver to steady state steering-wheel properties and to determine, firstly, the driver frame of reference, secondly; the difference thresholds for the perception of force and angle, and, thirdly, the rate of growth of sensations of force and angle.

The experiments were approved the Human Experimentation, Safety and Ethics Committee of the Institute of Sound and Vibration Research at the University of Southampton

3.1 Driver's frame of reference

Frames of reference provide means for representing the locations and motions of entities in space. There are two principal classifications for reference frames in spatial perception: the allocentric (a framework external to the person), and the egocentric (a frame- work centred on the person). For some tasks, the choice of reference frame may be merely a matter of convenience. In human spatial cognition and navigation the reference frame determines human perception. The haptic perception of steering-wheel position and motion is influenced by the spatial constraint imposed on the wheel, which can only rotate about a column.

In engineering terms, it is convenient to describe the motion of a steering wheel in a rotational frame of reference using steering-wheel torque and steering- wheel angle. However, drivers may use a different frame of reference when perceiving the feel of a steering system; they may perceive steering-wheel force rather than steering-wheel torque, and steering-wheel displacement rather than steering-wheel angle

Alternatively, drivers may use neither allocentric nor egocentric frames of reference and instead may employ some intermediate reference frame as suggested by Kappers

This experiment aims to test whether drivers sense steering-wheel force or torque, and whether they sense angle or displacement. The relationships between these properties are

T=rF (1) x=rB (2)

To investigate which variable is intuitively used by drivers, it is necessary to uncouple the relationship between rotational and translation frames of referece. This can be achieved by altering the radius of the steering wheel. It was hypothesized that, when asked to 'match' a reference condition using isometric steering wheels (i.e. wheels chat do not rotate)with varying radii, subjects would match either the force applied by the hand or the torque applied to the steering wheel. It was similarly hypothesized that,when using isotonic steering wheels (i.e. wheels that rotate without resistance to movement) with varying radu,