Summary and Conclusions

This page provides a brief summary of our results and main conclusions. More detailed accounts can be found in the published outputs of the project, as listed on a separate page.

Results

Returning to the three questions posed at the outset of the project, we made the following discoveries.

(a) Can static cues about human body movement influence lower levels of visual motion processing?

Although we replicated the published ‘implied motion after-effect’ (IMAE), results indicated that the IMAE was due to response or decision bias rather than sensory bias. In the paper we published to report these results, we argued that a propensity towards response and decision biases should not be viewed as artefactual, but as an integral part of all sensory decision-making in the face of uncertain visual information.

(b) How does the brain construct representations of the real-world pace or speed of human actions?

A series of experiments showed that judgements of the pace of human actions rely at least partly on relatively low-level retinal information in the form of responses in early visual channels tuned to image temporal frequency content. However, multiple lines of evidence also pointed to the involvement of high-level processes as well. These processes are involved in PLW perception and in the estimation of objective speed from retinal temporal frequency information. So both low-level and high-level processes contribute to judgements of real-world speed, in order to achieve velocity constancy. Changes in the relative sensitivity of the low-level processes are responsible for re-normalisation, which is a hallmark of perceptual constancies.

(c) What are the contributions of perceptual and decisional factors to visual judgements?

As mentioned in (a), the results of several experiments indicated that response/decisional factors can play a role in visual judgements. They make a strong contribution to the implied motion after-effect, and also to some extent to measures of locomotion adaptation.

Conclusions

Our judgements of the speed of real-world objects are not stable and fixed, but vary markedly depending on recent visual experience.

Multiple neural processes in the brain contribute to these judgements.

Inferences about mood, intention and so on based on movement speed cannot therefore be considered as completely reliable.