Handbook of Psychology, Volume 4: Experimental Psychology

302 Action Selection

response-stimulus interval (RSI) was 50 ms but not when it
was 500 ms.
Since Bertelson’s (1961) study, numerous, more detailed
investigations of sequential effects in choice-reaction tasks
have been conducted. First-order sequential effects are those
that involve the relation of the current trial to the immediately
preceding trial. The most common first-order effect is that the
response to a stimulus is faster when the S-R pair for a trial
is a repetition of the preceding S-R pair than when it is not.
In two-choice tasks, this repetition benefit is obtained only
when the RSI is short. At RSIs of 500 ms or longer, a benefit
for alternations over repetitions is typically found instead.
The repetition benefit is larger in tasks with more than two
choices, being an increasing function of the number of S-R
alternatives, and in these tasks a repetition benefit is found
even at long RSIs (Soetens, 1998). The first-order sequential
effects have been attributed to two processes, much like
those proposed for priming effects (Neely, 1977; chapter by
McNamara & Holbrook in this volume). At short RSIs, resid-
ual activation from the preceding trial produces automatic fa-
cilitation when the current trial is identical to it; at long RSIs,
strategic expectancy regarding the nature of the next trial pro-
duces faster responses for expected than unexpected stimuli
(Soetens, 1998). This expectancy is for the alternative S-R
pair in two-choice tasks, but for repetition of the same pair in
tasks with more alternatives.
Pashler and Baylis (1991) evaluated the locus of the repe-
tition benefit for tasks in which two stimuli were assigned to
left, middle, and right response keys operated by index, mid-
dle, and ring fingers of the right hand. Two of the stimuli
were digits, two were letters, and two were nonalphanumeric

symbols (e.g., & and #). Stimuli were mapped to responses

in a categorizable (e.g., digits-to-left response, letters-to-

middle response, and symbols-to-right response) or uncate-

gorizable (e.g., a digit and a letter to the left response, etc.)

manner. For both mappings, the repetition benefit occurred

primarily when the same stimulus was repeated and not

when only the response was repeated. This repetition bene-

fit for the same stimulus was not found when responses on

alternate trials were vocal and manual. Consequently, Pashler

and Baylis concluded that the repetition effects were at

the stage of response selection, with the normal response-

selection process being bypassed when the stimulus and re-

sponse were repeated.

In Pashler and Baylis’s (1991) experiments, a benefit for

response repetition alone tended to occur with categorizable

but not uncategorizable S-R mappings. Campbell and Proctor

(1993) verified this effect, showing a benefit of approxi-

mately 40 ms for response repetition alone with categorizable

mappings but not uncategorizable mappings. Their remain-

ing experiments showed that this response repetition benefit,

as well as the additional benefit for repeating the same stimu-

lus, could be obtained when the responses on successive tri-

als were made with different hands. In the critical conditions,

the stimuli were presented to the left or right of fixation on

alternate trials, with responses to the left stimulus made with

the three fingers on the left hand and responses to the right

stimulus made with the three fingers on the right hand.

A cross-hand repetition benefit was obtained when either

spatial or finger information was consistent across hands,

but not when both consistencies were eliminated. These

results imply that the response sets can be coded in terms of

Stimulus

Element

Stimulus

Encoding

rj Identity &

Program

Sj

Response

Identification: rk Identity

Retrieve

Program

rk

?

-table lookup

-search

-rule

-etc

Verification

rj = rk

Ye s

Congruent

Execute rj

Execute

rk

Abort rj

Incongruent

No

Figure 11.4 Illustration of the dimensional overlap model by Kornblum et al. (1990). The top route depicts automatic activation of

the corresponding response, and the bottom route depicts identification of the assigned response by intentional S-R translation.

Source:From Kornblum, Hasbroucq, & Osman (1990).