Perceived Structure and Search Efficiency: Investigating the Role of Plaid Composition and Grating Characteristics.

Plaids consist of two orthogonally oriented gratings. However, their structure may be perceived as a checkerboard with an oblique orientation or as two overlaid gratings. We used a visual search paradigm to investigate how plaids with different perceived structures influence search efficiency for determining whether a preattentive plaid-specific or grating-specific mechanism is involved in representing the plaid. Participants searched for a grating among plaids (Experiment 1) or a plaid among gratings (Experiment 2). Contrast (low vs. high), composed spatial frequency (SF) of the plaid (coherent vs. mixed), and target--distractor orientation relationship (component orientation-- aligned vs. structure orientation--aligned) were manipulated to vary the perceived structure of the plaid. Parallel search was observed when the target was a coherent checkerboard plaid, and orientation manipulation did not influence search efficiency. However, search performance was less efficient when the target plaid was perceived as overlaid gratings. When searching for a grating among plaids, low-SF gratings were located more quickly than high-SF gratings, regardless of the plaid distractor type. The results provide evidence for the existence of a preattentive plaid-specific mechanism that is distinct from the grating-sensitive mechanism. [ABSTRACT FROM AUTHOR]