A dynamic 1/f noise protocol to assess visual attention without biasing perceptual processing

Psychophysical paradigms measure visual attention via localized test items to which observers must react or whose features have to be discriminated. These items, however, potentially interfere with the intended measurement as they bias observers spatial and temporal attention to their location and presentation time. Furthermore, visual sensitivity for conventional test items naturally decreases with retinal eccentricity, which prevents direct comparison of central and peripheral attention assessments. We developed a stimulus that overcomes these limitations. A brief oriented discrimination signal is seamlessly embedded into a continuously changing 1/f noise field, such that observers cannot anticipate potential test locations or times. Using our new protocol, we demonstrate that local orientation discrimination accuracy for 1/f filtered signals is largely independent of retinal eccentricity. Moreover, we show that items present in the visual field indeed shape the distribution of visual attention, suggesting that classical studies investigating the spatiotemporal dynamics of visual attention via localized test items may have obtained a biased measure. We recommend our protocol as an efficient method to evaluate the behavioral and neurophysiological correlates of attentional orienting across space and time. Significance statementWhere (and when) we pay attention can be experimentally quantified via visual sensitivity: Attending to a certain visual signal results in better detection and feature discrimination performance. This approach is widely used, but poses an unrecognized dilemma: The test signal itself, typically a grating or letter stimulus, biases observers perception and expectations - and thus also the attention measurement. We developed a stimulus that manages without test items. The signal to measure attention is seamlessly embedded in a dynamic 1/f noise field, so that neither spatial nor temporal information about signal presentation is conveyed. Unlike with conventional approaches, perception and expectations in this new protocol remain unbiased, and the undistorted spatial and temporal spread of visual attention can be measured.