The simple reaction time to changes in direction of visual motion

Area of Science:

• Perception
• Human Factors
• Psychophysics

Background:

• Dzhafarov et al. proposed a model for reaction time (RT) to one-dimensional velocity changes.
• This model suggests a "subtractive normalization" process reinitializes motion detection.
• The model predicts RT is a function of the magnitude of velocity change: |V1-V0|⁻²/³.

Purpose of the Study:

• To test Dzhafarov et al.'s model for two-dimensional velocity changes.
• To investigate human reaction time to changes in motion direction.
• To propose an extension of the "subtractive normalization" hypothesis.

Main Methods:

• Subjects viewed a random dot pattern with changing motion direction.
• Motion direction changed by an angle α (6°–180°) at constant speed (4 or 12 deg/s).
• Subjects reacted to the direction change as quickly as possible.

Main Results:

• Reaction times (RTs) decreased as the angle of direction change (α) increased.
• RTs were shorter at 12 deg/s compared to 4 deg/s.
• Data were well-described by the function |V1-V0|⁻²/³ = (2Vsin(α/2))⁻²/³.

Conclusions:

• The "subtractive normalization" model successfully explains RT to two-dimensional velocity changes.
• An extended model assumes the velocity vector decomposes into orthogonal components.
• Explanations involving position or orientation cues were inconsistent with the data.