Echoic Memory

In a conceptual replication of Sperling's experiments, Darwin et al. investigated auditory sensory memory, or echoic memory. They simultaneously presented 3 letters to participants wearing headphones by playing the letters on either the left channel, the right channel or the both. They found similar results to Sperling's, as partial report produced better performance than whole report. However, the partial report advantage was not as large as with iconic memory. On the other hand, echoic memory did seem to last longer than iconic memory ( about 2-4 seconds for echoic v. less than 2 seconds for iconic).

Signal Detection Theory

Signal detection theory was formed first in information theory to deal with the idea of a receiver and a signal. The question of interest was: can the receiver detect the signal from the background noise?
Signal detection theory assumes that (a) the receiver (person) gathers information regarding the presence or absence of an event to (B) make a decision based on that information, which should result in a response of either "yes" or "no." The different categories are listed below :

Signal Detection Terms
	Signal + Noise	Noise
"Yes" response	HIT	FALSE ALARM
"No" Response	MISS	CORRECT REJECTION

The signal and noise can be represented by 2 distributions: the noise distribuation and the noise + signal distribution. The distance between the peaks of these distributions is a measure of the receiver's sensitivity. If the distributions are farther apart (they overlap very little), then the receiver is very sensitive to the distinction between them. Thus, the receiver should be able to easily detect signal in the noise.

However, signal detection theory also assumes that the receiver makes a decision about whether to respond or not. That decision is based on the criterion that the receiver sets. The criterion can be influenced by the costs and benefits of the possible responses (saying "yes" or "no"). If the cost of saying "yes" is high, then the receiver will likely have a relatively high criterion for saying "yes."

The power of signal detection theory is that it can apply to all 2 choice judgments, because all of those choices are about whether a signal is present or absent.