Aiming for the future: prospective action difficulty, prescribed difficulty, and Fitts' law

Area of Science:

• Human-Computer Interaction
• Cognitive Psychology
• Motor Control

Background:

• Fitts' index of difficulty (ID) quantifies task difficulty based on target size and amplitude.
• Understanding subjective difficulty perception is crucial for designing intuitive interfaces and predicting user performance.

Purpose of the Study:

• To investigate if Fitts' ID can serve as a reliable measure of subjective difficulty for prospective actions.
• To explore the underlying mechanisms of subjective difficulty estimation in the absence of movement.

Main Methods:

• Two experiments were conducted where participants estimated the difficulty of performing actions on presented target displays.
• Participants provided magnitude estimates of perceived difficulty without executing movements.
• Fitts' index of difficulty (log(2)(2A/W)) was systematically varied across trials.

Main Results:

• A strong positive correlation was found between Fitts' ID and subjective difficulty estimates.
• Results were consistent across different display scales, demonstrating the robustness of the findings.
• Nonlinearities in the relationship mirrored those in Fitts' law, suggesting a link to movement time prediction.

Conclusions:

• Fitts' index of difficulty is a valid indicator of subjective difficulty in prospective actions.
• Subjective difficulty perception likely involves monitoring internal feedforward control signals.
• Prospective difficulty estimation may rely on implicit mental simulations of movement parameters.