Iconic Memory and Visual Cognition Notes

Visual Memory Systems

  • Visual memory encompasses several systems, including iconic memory, working memory, and long-term memory.

Iconic Memory

  • Definition: Iconic memory is a brief, precategorical visual memory system that retains incoming visual stimulation for a very short duration.
  • Format: High-capacity memory that decays quickly. Characterized by:
    • Visible persistence: The perception of a stimulus continues for a short time after it has been removed.
    • Informational persistence: The ability to hold on to information for processing after the stimulus is gone.

Visible Persistence

  • Duration: Approximately 200 ms from stimulus onset.
  • Historical Observations:
    • Noteworthy thinkers such as Aristotle and da Vinci have previously noted the persistence of vision.
    • Segner's Experiment (1740): Demonstrated the phenomenon with rotating coal viewed as a continuous circle.
    • Movie Frame Rate: Explains why 24 frames per second create a fluid motion, as our vision fills in the gaps between frames.

Studying Visible Persistence

  • Researchers investigate how individuals perceive stimuli over time intervals. Key experiments involve:
    • Stimulus Duration: Presenting a series of stimuli and measuring response times and accuracy of perception based on the interval between stimuli.
    • Tasks: Distinguishing visual features, such as identifying which stimuli do not contain a specific characteristic (e.g., a black dot).

Quick Decay of Memory

  • Examination shows individuals can identify stimuli efficiently for intervals less than 100 ms but perform poorly after that, especially with complex stimuli.

Informational Persistence

  • Sperling's (1960) iconic memory procedure highlighted differences in whole and partial reporting accuracy.
    • Whole Report: Participants report all items in a brief display, typically recalling about 4.5 items accurately.
    • Partial Report: Cueing participants to recall a specific subset of items (e.g., a row) significantly improves accuracy, often reaching up to 100% when the cue is provided immediately after the stimulus.

Delays in Reporting

  • Performance in partial reporting diminishes with increased delay in the cue tone after the stimulus presentation (0-1 second). This suggests that informational persistence has a time limitation.

Key Findings on Iconic Memory

  • Visible persistence lasts about 200 ms; informational persistence extends to approximately 500 ms.
  • Iconic memory displays a high capacity but is largely unprocessed information.
  • Both forms decay quickly after the stimulus disappears, with neural activity declining in the visual system.

Iconic Memory vs. Afterimages

  • Experimentation: Investigations into whether subjects relied on afterimages rather than visual information. Results indicate participants do not use afterimages for reporting as expected with complementary color conditions.

Visual Working Memory

  • When eye movements occur, iconic memory is largely erased, and visual working memory takes over.
    • Saccadic Masking: The phenomenon where the visual cortex blocks incoming visual information during saccades (rapid eye movements).

Demo Day Overview

  • Preparation for a practical demonstration of visual cognition principles, schedule includes formation of groups and project deadlines.