Tony H. Reinhardt-Rutland, Reader in Psychology,
December 04, 2012

Schwebel (1) raises the issue of how auditory processing might contribute to safe negotiation of the roads by pedestrians. In particular, does the masking of relevant auditory information entail unnecessary danger? Almost coincidentally, a recent review (2) has considered possible technological developments that might provide useful supplementary information to aid drivers in avoiding collisions: potential sources might be auditory in nature.

The purpose of this note is to draw attention to psychophysical evidence for the potential of auditory information in such contexts. For those with normal or corrected-to-normal eyesight, visual information is almost certainly of primary importance in conveying potential collision - specifically, visual expansion of the viewed object, or "looming". The object - say, an automobile - may be moving towards the static observer; alternatively, the observer may be moving towards a static object. Also, both observer and object could be moving towards each other. In contrast, an unthreatening receding object undergoes visual contraction.

There is strong evidence of hard-wired sensory processing of visual motion: motion aftereffects are well-known illusions in the visual modality, whereby the observer perceives illusory motion of a static stimulus after viewing steady motion of that stimulus for a minute of so. The aftereffect of visual approach is substantially stronger than the aftereffect of visual recession: the sensory-systems of humans (and many other species) are much more sensitive to approach, almost certainly reflecting the survival value in avoiding damaging collisions (3,4).

An analogous asymmetry applies to the auditory modality: in this case, approach is conveyed predominantly by increasing sound-level, while the less critical recession is conveyed by decreasing sound-level. Growing -louder aftereffects are stronger than growing-softer aftereffects (5). However, there is a limitation to the effectiveness of audition in determining collision. In vision, most objects are rigid or near-rigid: objects varying in size - for example, inflating or deflating balloons - are unusual, so an assumption of rigidity with regard to vision is extremely plausible. However, in audition, analogous assumptions are weaker and more ambiguous. For example, many sounds are percussive: after a short rise-time, their sound-levels steadily reduce. Indeed, evidence suggests that compensation for this characteristic is necessary in measuring auditory aftereffects (5).

The clear inference to be drawn is that vision provides better evidence for collision than does audition. No doubt the latter is useful for the visually-impaired - and might be quite well-developed for this group. However, for the normal-sighted the ambiguity of auditory stimuli may be such that vision inevitably predominates in responding to motion-in -depth. Instead, the real issue of much auditory stimulation on the road - such as music presented over earphones, or via an automobile's sound- system - may be one of distracted attention.


(1) Schebel DC. Do our ears help us cross streets safely? Inj Prev 2012 10.1136/injuryprev-2012-040682.

(2) Spence C. Drive safely with neuroergonomics. Psychologist 2012; 18: 664-667.

(3) Scott TR. Lavender AD, McWhirt RA, Powell DA. Directional asymmetry of motion aftereffect. J Exp Psychol 1966; 72: 806-815.

(4) Reinhardt-Rutland AH. Perception of motion-in-depth from luminous rotating spirals: direction asymmetries during and after rotation. Perception 1994; 23: 763-769.

(5) Reinhardt-Rutland AH. Perceptual asymmetries associated with changing-loudness aftereffects. Percept Psychophys 2004; 66: 963-969.

Conflict of Interest:

None declared

Conflict of Interest

None declared