Signal Detection Theory – AP Psychology

Learning Objectives

Understand signal vs noise distributions

Identify four outcomes: Hit, Miss, FA, CR

Explain how criterion shifts affect outcomes

Relate d′ (sensitivity) to discrimination ability

Key Concepts

Noise: Background internal activity (no signal present)

Signal+Noise: When a real stimulus is present on top of noise

Criterion (β): Decision threshold — "Did I detect it?"

d′: Sensitivity — distance between distributions (higher = better detection)

Outcome Matrix

Hit: Signal present, say "Yes" ✓
Miss: Signal present, say "No" ✗
False Alarm: No signal, say "Yes" ✗
Correct Rejection: No signal, say "No" ✓

Colors

Noise distribution

Signal+Noise distribution

Criterion line

SDTPerceptiond′

d′:-

Criterion:-

Hit Rate:-

FA Rate:-

	Signal Present	Signal Absent
Say "Yes"	Hit -	False Alarm -
Say "No"	Miss -	Correct Reject -