CogLab - Stenberg Search Lab 22

Question 1

Background

Introduction

Answer 1

• researchers of memory believe that there exists a short-term memory (STM) system that holds information for a few seconds. If the information in STM is not transferred to long term memory (LTM) for more permanent storage, it vanishes
• As evidence of the existence of STM grew, researchers started to explore its properties. In a series of articles starting in 1966, Saul Sternberg developed an experimental approach to explore how information was retrieved from STM.

Question 2

Background

Basic approach of Sternbeg

Answer 2

• Participants were shown a short (one to six items) list of numbers and asked to memorize them
• putting them to memory, a probe number was shown
• The probe number was either one of the numbers in the list or a new number.
• The participant was to respond as quickly as possible, indicating whether the probe number was in the list or not.

Question 3

Background

Basic aim/hypothesis of Sternberg

Answer 3

• The response time of the participant should reflect the time spent searching STM to determine whether the probe number is part of the list. By varying the number of items in the list, Sternberg hypothesized that he could test several theories of STM search.

Question 4

What was stenberg results consistent with?

first result

Answer 4

• successive or serial search. Specifically, he found that response times grew linearly with increases in memory set size. For each additional item in the memory set, participants took (on average) an additional 38 ms to make their responses. Thus, it seems the probe item is compared one-by-one with each item in STM, and each comparison takes approximately 38 milliseconds.
  *

Question 5

General predictions

Answer 5

• If memory search requires consideration of each item in succession – a serial search – the response times should increase with memory set size because the participant will, on average, have to search through more items for larger set sizes.
• In contrast to a serial search, it is possible that there is a parallel search. For example, some neural network theories of STM suggest that every item in memory can be accessed simultaneously due to the parallel nature of search in these networks. If such a search took place in STM, the prediction is that response times would not vary as the memory set size increased.

Question 6

Findings of Stenberg search

Question 7

Sternberg conclusion final finding

Answer 7

STM is always exhaustive. That is, the cognitive processes responsible for searching STM for a particular item search through all items in STM before reporting whether the probe item is in memory or not.

Question 8

Instruction

Answer 8

• A fixation point will appear in the middle of the screen. After a second, a memory set consisting of 1, 3, or 5 digits will appear on the screen for 1.2, 3.6, or 6 seconds, respectively. Study the numbers and commit them to memory.
• The memory set will disappear and then a probe item will appear 1 to 3 seconds later. Your task is to determine whether the probe item was in the list of just presented numbers (respond present) or was not in the list (respond absent). Respond as quickly as you can.
• minimum of 60 trials in the experimental session.
• For each “Present” and “Absent” condition, 10 trials are presented for each memory set size. If you make a mistake (e.g., say the item was present when it was not), the trial will be repeated (with different numbers) later in the experiment. In this way, only response times for trials in which you were correct are used. If you find you are often making mistakes, you should try slowing down your responses and/or try harder. However, don’t be too slow in responding: slow trials will be repeated.

Question 9

Sternberg second result

Answer 9

• When he compared response times for probe “Present” and “Absent” trials (probe item was in the memory set or not, respectively), Sternberg found no differences in response times
• his finding is notable because an “Absent” response can be made only after all items in STM have been searched and found not to match the probe item. At first glance, it might seem that a “Present” trial could terminate as soon as the probe item is matched with the appropriate item in STM. With a self-terminating search, one would expect “Present” trials to be faster, but the data contradict this hypothesis.

Question 10

What methods did we employ in this experiment?

Answer 10

On each trial, you saw 1, 3, or 5 numbers for 1.2, 3.6, or 6 seconds (respectively). Then, 1 to 3 seconds later, a single number was shown. Your task was to indicate as quickly and as accurately as possible whether this probe number was in the list just presented.

The independent variable is the number of digits in the memory set (1, 3, or 5). The dependent variable is the speed with which you made a correct decision.

Question 11

What do we predict participants will do? Why?

Answer 11

• Your results are in the graph below which plots response time as a function of memory set size, with separate curves for “Present” and “Absent” trials.
• You should find that both curves increase with set size, and that the curves are nearly straight lines. S
• ternberg found that the “Present” and “Absent” curves were nearly superimposed, but you may not find that to be true. (Sternberg’s participants had more practice and were paid to be highly motivated.) Your data would agree with Sternberg’s general findings if your curves were parallel. If your curves diverge as set size increases, your data are not consistent with Sternberg’s general findings

Question 12

How robust is this effect? Are there limits to this effect?

Answer 12

Your results may differ because this lab doesn’t give you nearly as much practice as Sternberg’s original participants had.