C81MPR Practical Methods (Lab 2) Jonathan Stirk & Danielle Ropar

Sternbergs Study of Short Term Memory Storage

Introduction Researchers can use external measures to identify component cognitive processes Researchers can use external measures to identify component cognitive processes Two of the most important measures have been: Two of the most important measures have been: –(1) the study of errors in memory or problem-solving –(2) the study of reaction times or the time needed to perform a cognitive task

Studying Short Term Storage Sternberg (1966) proposed a method of studying how people search short- term memory Sternberg (1966) proposed a method of studying how people search short- term memory He used reaction times as his dependent variable He used reaction times as his dependent variable

Searching Short Term Memory Sternbergs experiment attempted to address two questions: Sternbergs experiment attempted to address two questions: –Do we search STM one item at a time (serially) or all at once (in parallel)? –Does the search stop when the item is located (self-terminating) or must it continue through the entire contents of STM (exhaustive)?

The Basic Task Suppose you are given a set of numbers to remember, and are permitted to rehearse them by saying them over and over to yourself Suppose you are given a set of numbers to remember, and are permitted to rehearse them by saying them over and over to yourself At various times you are given a number and must decide whether that number is one of the ones you were first given At various times you are given a number and must decide whether that number is one of the ones you were first given In order to do this, you must somehow search the items you are rehearsing in STM in order to decide whether the test item is among them In order to do this, you must somehow search the items you are rehearsing in STM in order to decide whether the test item is among them

Sternbergs Task The participant is given a list of from one to six digits The participant is given a list of from one to six digits –These digits are called the memory set –The participant is allowed to rehearse this list A few seconds later, the participant sees a single digit A few seconds later, the participant sees a single digit –This number is called the probe The participant must indicate whether the probe digit is (+ve probe) or is not (-ve probe) a member of the memory set The participant must indicate whether the probe digit is (+ve probe) or is not (-ve probe) a member of the memory set

Serial vs. Parallel Search If you search serially, then the more items there are to search, the longer it should take. If you search serially, then the more items there are to search, the longer it should take. –RT should increase as the memory set size increases. If you can search all the items at once, it should not matter how many there are If you can search all the items at once, it should not matter how many there are –RT should be the same for any memory set size (up to the capacity of STM). Does RT increase with memory set size or not? Does RT increase with memory set size or not?

Predictions for Serial vs. Parallel Search

Exhaustive vs. Self Terminating Search For a self-terminating search searching can cease as soon as the probe is found For a self-terminating search searching can cease as soon as the probe is found –More items in the memory set leads to longer search times For an exhaustive search search continues even if the probe is found. For an exhaustive search search continues even if the probe is found. –More items in the memory set leads to even longer search times. Negative probes always lead to exhaustive searches Negative probes always lead to exhaustive searches

Predictions for Exhaustive vs. Self Terminating Search Reaction Time (time to respond) Memory Set Size Probe absent (-ve probe, exhaustive search) Probe present (+ve probe, self- terminating search) 16 This graph is assuming a serial search strategy

Summary Sternberg (1966) makes two sets of predictions Sternberg (1966) makes two sets of predictions –One set of predictions focuses on RTs for different set sizes –One set of predictions considers the position in the list of the probe item by set size If Sternberg is correct we should be able to distinguish If Sternberg is correct we should be able to distinguish –Serial vs. Parallel Search –Exhaustive vs. Self-Terminating Search