The simple reaction time to changes in direction of visual motion

Abstract

Recently Dzhafarov et al. presented a model explaining data on simple reaction time (RT) to unidimensional velocity changes. The authors suggested that having a motion with an initial velocity V0, the velocity change detection system is reinitialized by means of a "subtractive normalization" process. Therefore, any abrupt change from V0 to V1 is detected as if it were the onset of motion with a speed equal to /V1-V0/. They derived that the RT is a function of /V1-V0/(-2/3). We tested this model for the case of two-dimensional velocity changes. Our subjects observed a random dot pattern that moved horizontally, then changed the direction of motion by an angle alpha in the range between 6 degrees and 180 degrees without changing the speed V. Speeds of 4 and 12 deg/s were used. The subjects reacted as quickly as possible to the direction change. The RTs asymptotically decreased with increasing alpha; with 12 deg/s speed the RTs were shorter than those obtained with 4 deg/s. It was shown that the data can be well described as a function of /V1-V0/(-2/3)=(2Vsin(alpha/2))(-2/3). An extension of the "subtractive normalization" hypothesis for the case of two-dimensional velocity changes is proposed. It is based on the assumption that the velocity vector V1 after the change is decomposed into two orthogonal components. Alternative explanations based on the use of position or orientation cues are shown to contradict the data.

Visual detection of motion speed in humans: spatiotemporal analysis by fMRI and MEG

“…The human RT to the onset of our visual motion stimulus changed with speed, which is in agreement with the results of previous psychophysical studies [Ball and Sekuler, 1980;Dzhafarov et al, 1993;Hohnsbein and Mateeff, 1992;Mateeff et al, 1995Mateeff et al, , 1999Smeets and Brenner, 1994], that is, the marked similarity in the value of ␥ (about 0.5) of equation (1) (see Results), considering that different visual motion stimuli were used in these studies. Although in two other studies, higher values (approximately 1.0) of ␥ were reported [Burr et al, 1998;Troscianko and Fahle, 1988], the reason could be due to the use of lower speeds as discussed by the authors [Burr et al, 1998] and of a speed range (0.3-2°/sec) narrower than ours (0.4 -500°/sec).…”

“…It has been hypothesized that RT can be described by equation (2): RT ϭ Tc ϩ Tv, where Tc is the time independent of visual stimuli (presumably related to motor preparation and execution) and Tv is the time that varies with visual stimulus conditions [Burr et al, 1998;Dzhafarov et al, 1993;Ejima and Ohtani, 1989;Mateeff et al, 1999;van den Berg and van de Grind, 1989]. According to this equation, Tv represents the time required by the visual system to detect motion in our study and is independent of other processes such as cognitive and motor execution processes.…”

Detection of motion onset and offset: reaction time and visual evoked potential analysis

“…This mechanism is called subtractive normalisation. Several later studies conWrmed that the initial motion vector is largely ignored when changes in velocity are detected (Amano, Nishida, & Takeda, 2006;Hohnsbein & MateeV, 1998;MateeV et al, 2000;MateeV, Genova, & Hohnsbein, 1999).…”

Transient activity in monkey area MT represents speed changes and is correlated with human behavioral performance

“…Finally, we note that the general psychophysical properties of velocity detection described by Dzhafarov et al (1993) have subsequently been shown also to characterize the detection of motion direction (Hohnsbein and Mateeff 1998;Mateeff et al 1999). Considering the tuning of MT neurons to speed and direction, it seems promising to investigate how transients in this area depend on more complex changes of motion and whether they can be decoded by a threshold model, too.…”