Zahra Hussain¹ (), Chinaecherem Nwigwe, Patrick Bennett; ¹University of Plymouth, ²University of Plymouth, ³McMaster University

We compared the effects of signal uncertainty in a detection task for two signals: simple sinusoidal gratings, and two-dimensional noise textures. This comparison was prompted by our observation that textures elicit a potentially different strategy for detection than gratings. Observers performed a two-interval forced-choice task in which signal type (gratings vs. textures) and signal uncertainty (one vs. five signals) varied across blocks. The gratings were 1 cycle/degree sinusoids at five orientations (0, 72, 144, 216, 288 deg), and the textures were five band-limited noise patterns (2-4 cycles/degree). Signals were embedded in Gaussian noise that was either fixed to a single sample for both intervals and all trials in a block (fixed noise; five observers), or varied across intervals and trials (variable noise; three observers). In the no-uncertainty condition, a single orientation or texture was used throughout a block of trials. In the uncertainty condition, the signal was sampled randomly from one of five variations on each trial. Observers performed twelve blocks per session (2 signals x 2 uncertainty conditions x 3 repetitions per condition; 50 trials per block), and contrast thresholds were measured in each block using QUEST+. For gratings, contrast thresholds were higher under uncertainty, and this effect was larger in variable than fixed noise. Interestingly, no uncertainty effect was was found for textures in either noise condition. This result supports the idea that signal uncertainty has distinct effects on the detection of detection of spatially complex and spatially predictable patterns. We currently are investigating how these uncertainty effects vary across a larger group of naive and experienced observers.