Abstract
Here we examine the relationship between the perception of heading and flow parsing. In a companion study we have investigated the pattern of dependence of human heading estimation on the quantity (amount of dots per frame) and quality (amount of directional noise) of motion information in an optic flow field. In the present study we investigated whether the flow parsing mechanism, which is thought to aid in the assessment of scene-relative object movement during observer movement, exhibits a similar pattern of dependence on these stimulus manipulations. Finding that the pattern of flow parsing effects was similar to that observed for heading thresholds would provide some evidence that these two complementary roles for optic flow processing are reliant on the same, or similar, neural computation. We found that the pattern of flow parsing effects observed does indeed display a striking similarity to the heading thresholds. As with judgements of heading, there is a critical value of around 25 dots per frame; below this value flow parsing effects rapidly deteriorate and above this value flow parsing effects are stable [see Warren et al. (1988) for similar results for heading]. Also, as with judgements of heading, when there were 50 or more dots there was a systematic effect of noise on the magnitude of the flow parsing effect. These results are discussed in the context of different possible schemes of flow processing to support both heading and flow parsing mechanisms.
Highlights
Motion of the image of an object across the retina indicates relative movement between the object and the eye
We have investigated the dependence of flow parsing on both the quantity and quality of optic flow information
In addition below the critical level the effect of flow quality on flow parsing is seen to diminish with no difference in the size of the effect between the different noise levels at the lowest value of flow quantity tested
Summary
Motion of the image of an object across the retina indicates relative movement between the object and the eye. The relative movement may have arisen due to movement of the object (Figure 1A), movement of the eye (Figure 1B), or a combination of the two (Figure 1C). The role of nonvisual information in distinguishing between retinal movement due to the movement of the observer (“re-afference”) from retinal motion due to movement of objects in the environment (“exafference”) was described and investigated by von Holst (e.g., von Holst and Mittelstaedt, 1950) and explored further by Wallach (1987 for a review) and Gogel (1990 for a review). We have been investigating whether retinal information, optic flow (the global patterns of retinal motion that are characteristic of self movement), can be used to distinguish retinal motion due to self-movement from retinal movement due to object movement (Rushton and Warren, 2005; Rushton et al, 2007; Warren and Rushton, 2007, 2008, 2009a,b; Warren et al, 2012)
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