The reason 0° is easy while other relative phases are hard is that the requisite information is detected most readily at 0°. This test predicts that if a participant were to improve their ability to detect the requisite information then their movement stability would improve.
There were 12 participants. Half the participants were assigned to the Experimental Group and half to the Control. There were two types of experimental task: two alternative forced choice (2AFC) judgements, and coordinated rhythmic movement. There were then two types of session:
1. Assessment sessions consisted of both judgement trials (at both 90° and 180°) and movement trials (moving at 0°, 90°, and 180°). There was no feedback.
2. Training consisted only of judgement trials at 90° with feedback.
The Experimental group did three assessment sessions and up to 14 training sessions. The Control group did three sessions of movement trials, with no training or feedback.
Judgements (Perceptual Ability)
Participants had to identify a target phase of 90° in a pair of displays. Participants then trained with progressively harder perceptual discriminations around 90° with feedback.
Movement Stability (Baseline, Post Training and Retention)
Participants used a joystick to coordinate the movement of two dots on a screen at three relative phases. Participants were instructed to move so as to produce a mean relative phase of 0°, 180°, or 90°, three trials of each.
A repeated measures ANOVA was used to check the significance between the two groups. Significant differences were found in the experimental group which shows that perceptual training was successful. The movement task found that only participants in the Experimental group improved their movement stability across sessions and this improvement was restricted to 90°.
To conclude participants in this experiment improved their movement stability at 90° following training to improve their perceptual ability at 90°. Also improved perceptual discrimination of 90° led to improved performance in the movement task at 90° with no training. The improvement persisted until Retention without further exposure to either task.