2 EFFECTS OF CONTEXT ON THE PRESENCE ABSENCE OF CONNECTING SEGMENTS

Stimulus A consisted of two proximal brackets with colinear lines sepa rated by small gaps. Stimulus B was a square-like rectangle produced b y inserting connecting segments into the gaps. Stimulus A was frequent ly represented as B (i.e., as closed). Following Pomerantz and Pristac h (1989) and Treisman and Paterson (1984), perhaps A produced a closur e emergent feature that was salient but otherwise independent of other features. However, adding the same two vertical lines (context) to bo th A and B produced a contrasting division outcome, even though the pu tative closure emergent feature was an element of the A+context stimul us, and even though it matched a physical feature of the B+context sti mulus. Therefore, this emergent feature did not produce the closure. T wo additional experiments indicated that the two context lines made th e two connecting segments more visible-a context-produced increase in visibility occurred that is not comparable to other known evidence of perceptual improvement. This greater visibility also indicates that th e division was not due to the two context lines inhibiting the percept ion of the two connecting segments, and the closure was not due to goo d continuation.