A new approach for the study of visual orientation perception and decisions

Orientation and motion are arguably the most studied visual features in psychophysics and perceptual decision-making (PDM). Despite being processed by diverging brain mechanisms, orientation and motion share similar mechanistic and computational underpinnings (Clifford, 2002; Moon, Tadin & Kwon, 2022). Motion perception research has benefited tremendously from the random dot motion task (RDM) and associated coherence manipulations (Newsome & Pare, 1988). RDM is linked to significant advances in neurophysiological and psychophysical understanding of motion and has helped launch seminal work in PDM (Roitman & Shadlen, 2002). Aiming to develop a corresponding stimulus for orientation research, we focused on the key properties of RDM: signal-to-noise coherence manipulations and limited lifetime. For RDM, the features were 50 moving dots, with signal dots moving coherently in the target direction and noise dots moving in random directions. For the novel dynamic orientation task (DOT), signal orientations were component gratings with a fixed orientation, while noise component gratings had randomly chosen orientations. All gratings had random phases, small variations in spatial frequency were added together and normalized to 100% peak contrast. Both dots (RDM) and component gratings (DOT) had staggered, limited lifetimes of 250ms. For DOT, the result was an oriented stimulus with fluid-like dynamics. Using both tasks, we conducted parallel PDM experiments using reaction time (RT) and duration threshold approaches. Results showed that RDM and DOT have similar dependence on coherence. Next, we built a variation of the drift-diffusion model that, with no free parameters, predicts duration thresholds from RT data. Data for both RDM and DOT aligned precisely with predictions. Notably, a separate experiment with a conventional orientation task did not show this correspondence. In summary, we introduce a novel orientation stimulus that closely mirrors RDM. DOT might help open new venues of research into PDM and into similarities of motion and orientation.