Notes on Sensory Memory – Iconic and Echoic

Sensory Memory Overview

• Brief, high-capacity stores that hold sensory information for a very short time to allow perception and processing.
• Functions: provides time for perceptual processes, information is briefly available for attention and encoding into processing systems.
• Key idea: information transitions from sensory memory to short-term/working memory and eventually long-term memory; information not attended-to is rapidly lost.

Iconic Memory

• Visual sensory store (iconic SM)
• Duration: $0.1$ s
• Capacity: up to $12-16$ items
• Classic findings:
  • Sperling (1960): tachistoscope, brief presentation (~50 ms) shows high capacity but rapid decay; partial report yields more information than whole report.
  • Maximum reportable items: ≈ $4$ under standard conditions.
  • Averbach & Sperling (1961): pre/post field lighting effects: pre/post dark has little interference; light pre/post reduces iconic memory more quickly.
• Loss mechanism: decay and interference; pre/post cues influence the amount retained.
• Role: preserves raw visual input for a fraction of a second to enable encoding and integration.

Echoic Memory

• Auditory sensory store (echoic SM)
• Duration: $3-5$ s
• Capacity: up to $4-5$ items
• Classic findings:
  • Darwin et al.: partial report > whole report; longer duration than iconic; capacity around ~5 items.
  • Auditory cueing with multiple channels (e.g., three-ear task) shows reporting from attended channel after brief delays.
  • Findings summarized as: longer persistence than iconic, but smaller capacity.
• Loss mechanism: decay and interference from nonattended auditory input; timing of cues affects reporting.
• Role: maintains auditory information long enough to compare and select information for processing.

How SM fits into Information Processing

• Flow: External sensory input → Sensory Memory → Attention → Short-Term/Working Memory → Long-Term Memory
• SM provides a brief, literal snapshot that buys time for attention and encoding into STM/LTM.

Comparison: Iconic vs Echoic Memory

• Iconic SM: visual, $0.1s$ duration; large capacity (approx. $12-16$ items); fades quickly via decay/interference.
• Echoic SM: auditory, $3-5s$ duration; smaller capacity (approx. $4-5$ items); persists longer, supports sustained processing.

Mechanisms of Information Loss from SM

• Decay: time-based loss if not attended/encoded.
• Interference: new sensory input overwrites or disrupts existing items.
• Displacement: limited capacity leads to loss of prior items.
• Lost cues: retrieval depends on cues that may be unavailable.

Evidence and Models (Key Experiments)

• Sperling (1960): tachistoscope; partial report reveals more information than whole report; vivid short-term storage.
• Averbach & Sperling (1961): brightness of prefield/postfield affects interference; dark fields preserve more items briefly.
• Darwin, Turvey, & others (1960s): echoic memory shows longer duration with cued reporting; capacity around 5 items.
• Glucksberg & Cowan (1970): shadowing task with cue delays shows auditory memory decay over a few seconds; spontaneous digit detection remains low.

Quick Takeaways for Exam

• SM holds sensory input briefly to enable processing and transfer to STM/LTM.
• Iconic memory: visual; duration $0.1s$; large capacity; partial reporting reveals substantial residual information.
• Echoic memory: auditory; duration $3-5s$; smaller capacity but longer persistence than iconic.
• Key experiments: Sperling partial/whole report; Averbach & Sperling; Darwin et al.; Glucksberg & Cowan.