LOCATION AND LINE ORIENTATION AS DISTINGUISHABLE PRIMITIVES IN SPATIAL VISION

In geometry the same parameters define a straight line segment as its two endpoints, yet the human observer's perception of spatial relation s can differ depending whether an actual line is shown or merely its t erminators. Experiments are reported that demonstrate that the positio n and orientation senses can be largely decoupled. Because both point localization and line orientation each in its own way has a quality of immediacy, yet manifests high performance in the hyperacuity range, b oth must be regarded as a primitive each with its own neural processin g mechanisms. This can give rise to perceptual dissonances (visual ill usions) of which one example is analysed.