Academic journal article Attention, Perception and Psychophysics

Visual Orienting in Dynamic Broadband (1/F) Noise Sequences

Academic journal article Attention, Perception and Psychophysics

Visual Orienting in Dynamic Broadband (1/F) Noise Sequences

Article excerpt

Visual orienting has typically been characterized using simple displays-for example, displays with a static target placed on a homogeneous background. In the present study, visual orienting was investigated using a dynamic broadband (1/f) noise display that should mimic a more naturalistic setting and that should allow saccadic orienting experiments to be performed with fewer constraints. In Experiment 1, it was shown that the noise movie contains gaze-attracting features that are almost as distinct as the ones measured for (static) real-word scenes. The movie can therefore serve as a strong distractor. In Experiment 2, observers carried out a luminance target search that showed that saccadic amplitude errors were substantially higher (18%) than the ones measured in simple displays. That error is certainly one of the primary factors making gaze-fixation prediction in complex scenes difficult. Supplemental figures for this study may be downloaded from http://app.psychonomic-journals.org/content/supplemental.

Visual orienting has predominantly been investigated on homogeneous backgrounds with well-defined targets (see, e.g., Findlay & Gilchrist, 2003; Roos, Calandrini, & Carpenter, 2008); for example, a saccade is made from a central fixation cross toward a peripheral target of sufficiently high contrast. Such simple, highly controlled conditions are suitable to accurately determine parameters and dependencies such as saccadic latency toward a target, the dependence of latency on target parameters, target detectability in the periphery, and so on. How those parameters and dependencies change when more complex visual input is presented has been investigated only marginally. Analogously, Roos et al. even made a distinction between evoked saccades, the ones that are triggered in laboratory conditions, and spontaneous saccades, the ones that are triggered when freely viewing real images. Their analysis concentrated primarily on intersaccadic intervals. The orienting experiments mentioned so far were carried out with a "static" observer. Visual orienting is also investigated with "dynamic" observers to determine visual selection during daily activities such as tennis playing or walking through the forest (e.g., Einhäuser, Rutishauser, & Koch, 2008; Land, Mennie, & Rusted, 1999). Such experiments are beneficial for gaining a more detailed understanding of (spontaneous) saccadic target selection during actions, but they do not allow for the control of the visual environment to investigate precise orienting behavior in response to targets-for instance, how accurately a target is foveated during search. Our approach to the analysis of visual orienting aimed between the static and dynamic conditions: On the one hand, we desired control over the stimulus, and for that, the observer was preferably static; on the other hand, we wanted a stimulus that could possibly mimic the same degree of attraction (or distraction, depending on task) as that experienced during "free moving"-a simulation of the dynamic condition. For this purpose, we generated a movie based on dynamic broadband noise, which was displayed on a typical experimental CRT monitor. The broadband noise had an inverse frequency amplitude spectrum (1/f ), similar to the amplitude spectrum of natural images (Field, 1987). This allowed us to investigate saccadic orienting properties under closeto- naturalistic conditions.

Our first goal was to characterize visual selection in those noise movies-specifically, to elucidate whether, and to what degree, the dynamic 1/f movie stimulus provided preferred features of fixation selection. From scenefixation studies, it is known that there exists a preference for high contrasts (see, e.g., Parkhurst & Niebur, 2003; Reinagel & Zador, 1999; Tatler, Baddeley, & Vincent, 2006). One may therefore wonder whether this contrast preference also exists in a mere 1/f display (in our case, a movie). To investigate this question, observers merely performed free viewing in Experiment 1. …

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