                          
                          
                          Details of the design

 
 
 The present experiment is a replication of the original experiment done by 
 Saul Sternberg in 1966, 1967 and 1969(see references). Sternberg's study 
 deals with the question of "how is symbolic information retrieved from 
 recent memory" (Sternberg, 1966). Many researchers in the area held that 
 STM information is immediately available to the consciousness. Sternberg 
 showed that not only retrieval is not immediate, but he also discovered 
 an involuntary 'mechanism' which scans the content of the STM. Sternberg 
 even showed that this scanning processes proceeds in a serial manner at the 
 speed of about 38 milliseconds per item and that the process is exhaustive 
 (as opposed to self-terminated) and thus automatic. How did Sternberg 
 describe the scanning mechanism in such detail, a feat not common in 
 psychological research. 







 
 Sternberg used recognition reaction time design. He presented subjects with 
 a list of digits within the capacity of the STM store (1-6 digits). He called 
 the digits presented in each trial a positive set. Two seconds after the last 
 digit of the positive set was presented a target digit was shown. Subjects 
 were expected to respond by pressing one of the two buttons. One button 
 indicates a positive response (i.e. 'the target digit was a part of a 
 positive set') while the other button indicates negative response (i.e. 'the 
 target digit was not in the positive set'). Subjects were required to perform 
 at the accuracy level close to 100 %. Sternberg was not interested in 
 accuracy but in the reaction time needed for a correct response. 
 
 What kind of inferences did he make on the basis of that information?

 First, he looked at how the size of the positive set affects the reaction 
 time. Here he found a linear function. This means that reaction time 
 increased fairly regularly with introduction of each additional digit. A 
 linear function can be expressed as an  equation. The equation Sternberg 
 obtained from his data was RT = 37.9 N + 397. Number 37.9 represents the 
 slope of the function, or, in other words introduction of each additional 
 digit 'N' produced a 37.9 milliseconds delay in response. 
 
 
 
 
 Second, Sternberg looked at the data from positive and negative trials. 
 Common sense would lead us to conclude that reaction times would be shorter 
 on the positive trials (trials where a target digit was a part of the 
 positive set) than in the negative trials (the trials where the target digit 
 was not a part of the positive set). The reason is of course that in the 
 negative trial one would have to scan the entire positive set held in the 
 STM, while in the case of the positive trial scanning process would be 
 terminated after the match is found. As match is found after, on average 
 50 % of the digits were scanned, one would expect that positive trial 
 reaction is on average twice shorter than the negative trial. Surprisingly, 
 then no such trend was discovered in the actual data. RT in the positive and 
 negative trials was about the same, which led Sternberg to conclude that the 
 process is automatic and exhaustive. That means that each time a search is 
 initiated the entire set is scanned. 

 Therefore, Sternberg discovered an STM-scanning mechanism whose basic 
 characteristics are high-speed, high level of accuracy and automacity.

 Procedure:

 Present cue ("+")
 Pause for 500 ms.
 Present stimuli (stimulus duration: 1800 ms.)
 Sound a tone after the last stimulus (200 Hz.)
 Pause 2000 ms.
 Present Target
 Get response

