Increasing confidence in vergence as a cue to distance

Multiple cues contribute to the visual perception of an object's distance f rom the observer. The manner in which the nervous system combines these var ious cues is of considerable interest. Although it is accepted that image c ues play a significant role in distance perception, controversy exists rega rding the use of kinaesthetic information about the eyes' state of converge nce. We used a perturbation technique to explore the contribution of vergen ce to visually based distance estimates as a function of both fixation dist ance and the availability of retinal information. Our results show that the nervous system increases the weighting given to vergence as (i) fixation d istance becomes closer; and (ii) the available retinal image cues decrease. We also identified the presence of a strong contraction bias when distance cues were studied in isolation, but we argue that such biases do not sugge st that vergence provides an ineffectual signal for near-space perception.