In the present study, we chose to focus on reaction times to investigate how attention is allocated by default across 2D space during a simple pursuit task, without explicit manipulation of attention, e.g., through cues. Many studies have used reaction times as a behavioral correlate of attention with the following logic: if certain spatial locations are attended, a target appearing at that location should be detected faster, leading to faster reaction times, compared to targets flashed at non-attended locations (Findlay,
2009; Hoffman & Subramaniam,
1995; Posner,
1980; Shepherd et al.,
1986). Previous studies on pursuit have shown a decrease of reaction times ahead of pursuit compared to behind pursuit (Blohm et al.,
2005; Kanai et al.,
2003; Tanaka et al.,
1998; van Donkelaar & Drew,
2002). These studies indicate that, when there is no specific task or location to be attended, attention is by default allocated ahead of pursuit. However, there are a number of questions that remain unanswered. First, it remains unclear how attention is allocated during pursuit across two-dimensional (2D) space, i.e., across both distance and direction. Studies have shown that both saccade reaction times (Blohm et al.,
2005; Kanai et al.,
2003; Smeets & Bekkering,
2000; Tanaka et al.,
1998) and manual reaction times (van Donkelaar & Drew,
2002) are shorter to targets presented in the direction of pursuit compared to targets presented in the opposite direction. Some of these studies presented targets only along the horizontal meridian (Tanaka et al.,
1998; van Donkelaar & Drew,
2002), implying that attention may be constrained along a narrow horizontal range and following the pursuit path (
Figure 1A). Other studies presented targets at different directions relative to pursuit and found that saccade reaction times were shorter in some or all directions ahead of pursuit (Blohm et al.,
2005; Kanai et al.,
2003). Their results could be interpreted as a focus of attention ahead of pursuit (
Figure 1B) that is somewhat diffuse or a large overall bias in the entire field ahead of pursuit (
Figure 1C). The focus of attention hypothesis is also supported by van Donkelaar and Drew (
2002) who showed that
manual reaction times are reduced shortly ahead of pursuit but increase further ahead. On the other hand, other studies showed a decrease of
saccadic reaction times at both short (Kanai et al.,
2003) and at further (Tanaka et al.,
1998) distances ahead suggesting that attention may bias the entire visual field ahead of pursuit (
Figure 1C). In summary, the results of these studies are inconclusive because they were limited by a small set of potential target locations. Furthermore, the saccade reaction time studies produced conflicting results both with each other, and with those studies that used manual reaction time as a readout of attention allocation during pursuit, possibly because the experimental conditions were different in the different studies.