Reading focus
Syllabus: How Do We Perceive the World?
Reconsider an affordance as a probability of success rather than a single cutoff. Bring the opening distinction between sensitivity, criterion, and payoffs to the interpretation of action decisions.
A question to consider. If a person refuses a passage that they could sometimes negotiate, what would distinguish a mistaken judgment from a sensible response to variable ability and costly failure?
Why this reading
An action may succeed on some attempts and fail on others. Franchak and Adolph ask how acknowledging that variability changes the measurement of action possibilities and the interpretation of perceptual decisions.
Before you read
A psychometric function can describe success probability across doorway widths or slope angles. Its threshold locates a specified probability; its slope describes how rapidly performance changes. Actual ability, judged ability, and willingness to attempt an action are distinct quantities.
Read for
- Compare a sharp possible–impossible boundary with a graded success function.
- Examine the reanalyses and developmental examples, asking what body dimensions, experience, and trial sampling explain.
- Trace how variability and the consequences of failure affect the interpretation of cautious choices.
Consider afterwards
- Two people refuse the same gap, but one has a lower probability of crossing it successfully. What measurements would distinguish equal perceptual accuracy from different safety margins?
Editorial context
The paper combines a measurement proposal, reanalyses, and examples from several tasks and ages. It does not show that one function describes every action or that all observers accurately perceive their success probabilities. A cutoff is a measurement convention; it should not be mistaken for a fixed boundary in the person’s capabilities.