Chapter 6: Speed, Accuracy, and Timing Quiz

Speed-Accuracy Trade Off

• Accuracy decreases as movement speed increases; achieving both requires a compromise.
• Slower movements yield higher accuracy, while faster movements tend to be less accurate.

Fitt's Law

• Movement time (MT) in aiming tasks relates to the logarithmic formula Log2(2A/W); where A is amplitude (distance) and W is target width.
• This law helps predict the time required to aim accurately.

Index of Difficulty (ID)

• Defined as ID = Log2(2A/W); measures the difficulty of a movement in Fitts' tapping task.

Amplitude (A)

• Represents the distance between two target centers in aiming tasks.

Width (W)

• Indicates the size of the target involved in aiming tasks.

Predicting MT Using Fitt's Law

• MT can be calculated using the formula MT = a + bLog2(2A/W).

Effective Target Width (We)

• Represents the variability of movement endpoints about a target, which affects perceived target size.
• Calculated as the within-subject standard deviation of movement distances over multiple attempts.

Schmidt's Law

• Suggests consistency in aiming errors across different combinations of movement amplitude and MT that maintain a constant average velocity.

Linear Speed-Accuracy Trade Off

• Explains that increases in amplitude and decreases in MT can occur simultaneously while maintaining movement accuracy.

Variability in Rapid Movements

• Rapid movements lead to more errors primarily because there is insufficient time for feedback and corrections.
• The inconsistency in muscle activation processes contributes to this variability.

Understanding Noise in Fast Movements

• "Noise" refers to inconsistencies in motor program execution, leading to discrepancies in intended forces and resultant movements.
• Noise tends to increase with greater force application, particularly beyond 70% of maximal force.

Noise Example: Hammer and Nail

• In hammering a nail, various muscle groups exert forces at different angles; inaccuracies in force application can lead to missing the target.

Speed Increases and Errors

• Forces from multiple muscles determine movement trajectory; as more force is required for rapid movements, variability also increases, leading to potential errors.

Relationships Between Movement Speed, Distance, and Accuracy

• MT increases when either the target amplitude (A) increases or the target width (W) decreases.

Woodworth's Two-Component Model

• Describes the process of hitting a target comprising two phases:
  • Initial ballistic phase
  • Homing in phase

Exceptions to the Speed-Accuracy Trade Off

• Certain scenarios where S-A trade-off does not apply include:
  • Extremely rapid and forceful movements
  • Targets affected by optical illusions
  • Critical timing accuracy requirements

Forceful Movements Exception

• Very forceful movements yield lower variability due to maximal effort, resulting in increased accuracy.
• An inverted-U relationship exists, with least accuracy at moderate force levels.

Visual Illusions as an Exception

• Optical illusions can enhance perceived accuracy or yield increased errors due to brain misinterpretation.

Movement Timing as an Exception

• Time-sensitive movements are performed more accurately in shorter durations, with reduced opportunities for noise interference.
• Halving MT can also cut timing errors in half.