Form discrimination: features or invariants?

Does form discrimination rely on feature analysis, as the indirect theory of perception supposes, or on affordances (behavioural meanings specified by invariant patterns), as direct theory states. Subjects were to indicate the position of a target in a perspective rendering of a plane, displayed for 100 msec. in a large screen projection. In one of the conditions the target disrupted the plane, in the other it did not. Although targets of the two conditions shared the same features, the disruptive targets were discriminated more often than the nondisruptive targets. This result supports the direct approach to perception which states that a perceiver discriminates behaviourally relevant patterns rather than geometrical properties.