Modulating Fitts's Law: perceiving targets at the last placeholder

Area of Science:

• Cognitive Psychology
• Human-Computer Interaction
• Motor Control

Background:

• Fitts's Law typically predicts longer movement times (MTs) with increased movement amplitude.
• A known modulation shows shorter MTs to targets in the final position of a structured perceptual array with placeholders.
• The cause of this Fitts's Law modulation has remained unclear, particularly whether it stems from perceptual or motor planning mechanisms.

Purpose of the Study:

• To investigate the perceptual basis of the Fitts's Law modulation observed with targets in structured arrays.
• To determine if perceptual factors such as interference, processing speed, or representational quality at the final array position contribute to the modulation.

Main Methods:

• Three experiments were conducted to test perceptual hypotheses.
• Experiment 1 used diminished placeholders to assess perceptual interference.
• Experiments 2 and 3 employed target detection and masked letter discrimination tasks, respectively, to evaluate perceptual processing speed and quality.

Main Results:

• Diminished placeholders did not eliminate the Fitts's Law modulation, ruling out perceptual interference.
• Reaction times and accuracy measures indicated no significant speed-up or enhancement in perceptual processing at the final array position.
• The observed modulation in movement times was not attributable to changes in visual processing effectiveness.

Conclusions:

• The Fitts's Law modulation in structured arrays is not driven by perceptual mechanisms like reduced interference, faster processing, or improved representation quality.
• These findings suggest the locus of the modulation is likely within the motor planning stage.
• The study indicates that perceptual factors do not explain the deviation from Fitts's Law in this context.