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

Abstract

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 paradigm, 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 paradigm as an efficient method to evaluate the spatial and temporal spread of visual attention.

Foveal vision anticipates defining features of eye movement targets

“…To generate the background noise images, we applied a fast Fourier transform to uniform white noise, multiplied the noise spectrum with its inverse radial frequency, and transformed it back using an inverse fast Fourier transform ( Hanning and Deubel, 2022 ; Hanning et al, 2019 ; Hanning and Deubel, 2021 ). For Experiment 1 and Experiment 3, 34 noise images (17 for the staircase and main experiment, respectively) were generated for each observer and session.…”

“…At the same time, the stimulus probing performance in the center of gaze must be inconspicuous enough not to interfere with saccade programming ( Rolfs et al, 2011 ; Hanning et al, 2019 ). In light of these considerations, we smoothly embedded our stimuli in a dynamic stream of full-screen, 1 /f noise images ( Hanning and Deubel, 2022 ; Hanning et al, 2019 ; Hanning and Deubel, 2021 ; see Materials and methods). Observers maintained fixation in the screen center while the images flickered at a temporal frequency of 20 Hz ( Figure 1A ).…”

Foveal vision predictively sensitizes to defining features of eye movement targets

“…Seven human observers (five females, seven right-handed, four right-eye dominant, one author) aged 22 to 34 years (Mdn = 28.0) participated in the experiment. Since we could not derive effect-size estimations from prior studies, we chose a sample size within the typical range of experiments investigating pre-saccadic attention shifts [41,22] . Normal (n = 4) or corrected-to normal (n = 3) visual acuity was ensured at the beginning of the first session using a Snellen chart (Hetherington, 1954) embedded in a Polatest vision testing instrument (Zeiss, Oberkochen, Germany).…”

“…To generate the background noise images, we applied a fast Fourier transform to uniform white noise, multiplied the noise spectrum with its inverse radial frequency, and transformed it back using an inverse fast Fourier transform [21,22] . A total of 34 noise images (17 for the staircase block; 17 for the main experiment) were generated for each observer and session before the respective task.…”

“…At the same time, the stimulus probing performance in the center of gaze must be inconspicuous enough not to interfere with saccade programming [20,21] . In light of these considerations, we smoothly embedded our stimuli in a dynamic stream of full-screen, 1/f noise images [22] (see Methods). Observers maintained fixation in the screen center while the noise images flickered at a temporal frequency of 20 Hz (Figure 1A).…”