Chapter 2 Chapter Summary

Chapter Overview:

We are constantly inundated with sensory information. Much of that information is not useful but we still need access to it in case it is important.

The early cognitive models of information processing, including the modal model of memory, proposed a concept of sensory memory as storage for all sensory information it to be available to us for processing if required. Sensory memory was believed to be large capacity, modality-specific memory stores. Each modality had its own sensory register. The most commonly studied are iconic memory (visual sensory memory) and echoic memory (auditory sensory memory).

The most well-known studies of sensory memory were conducted by George Sperling in 1960 on iconic memory. Participants in these studies saw a 3 × 4 matrix of letters for a brief interval (about 50 ms). Recall was poor in the whole-report paradigm (mean of 4.6 letters). But accuracy was significantly higher when participants only had to recall one row even though they did not know which row was targeted until the display had disappeared. This partial-report advantage persisted up until a 500 ms delay in cueing the row. These findings led Sperling to conclude that all visual information is available in iconic memory but only for up to 500 ms.

Other studies conducted by Sperling (1960) suggested that the information in iconic memory was pre-categorical, that is, not yet identified as belong to a particular type.

More recent research though has contradicted Sperling’s notion of iconic memory as being a vast, rapidly-fading, pre-categorical memory store independent of short-term memory (STM). In fact, most of the partial-report advantage is now thought to be the result of output interference. Other newer research has focused on the function of iconic memory and has found evidence that it improves decision-making accuracy especially after a slight delay.

Echoic memory, pre-categorical auditory memory that lasts for about two seconds, has also been extensively studied. Early studies on echoic memory showed a partial-report advantage albeit smaller and longer lasting than with iconic memory. Other research using the serial position paradigm found evidence of a pre-categorical acoustic store (PAS), in essence the same as echoic memory. But like iconic memory, newer evidence called into question this view of echoic memory, especially the idea that it was pre-categorical.

The phenomena of stimulus persistence and information persistence are now more popular explanations of Sperling’s (1960) and other research findings. Stimulus persistence is residual neural activity lasting for about 100 to 200 ms after a stimulus is removed. While stimulus persistence can explain some of the previous findings, it is too brief to account for the partial-report advantage and the suffix effect. On the other hand, information persistence is the availability of information about an item that persists after it is removed. Information persistence is believed to be non-sensory and the result of STM.

In Di Lollo’s (1980) classic study on stimulus persistence, participants were briefly shown two displays of 12 dots randomly placed in a 5 × 5 matrix and asked to identify the dot-free spaces. He found that when the displays were shown quickly together (less than 100 ms), participants perceived one display and it was easy to identify the area without a dot. Later, Irwin and Yeomans (1986) replicated the partial-report study but varied the stimulus duration from 50 ms to 500 ms. No effect of stimulus duration was found on the accuracy of recall suggesting that stimulus persistence was not being used in this task. Instead, they proposed that information persistence (from STM) explained the partial-report advantage.

Further evidence from neuroscience supports the notion that stimulus persistence and information persistence do exist and are anatomically distinct.

Learning Objectives:

Having read this chapter, you will be able to do the following:

1. Distinguish between the concepts of iconic memory, sensory persistence, and information persistence.
2. Describe Sperling’s (1960) paradigm for studying iconic memory.
3. Describe the results of Sperling’s (1960) partial and whole report experiments.
4. Critique Sperling’s (1960) model of iconic memory.
5. Describe the modality effect and the suffix effect.