The warning stimulus as retrieval cue The role of associative memory in temporal preparation
Sander A. Los a,* , Jurre Nieuwenstein a , Anass Bouharab a , David J. Stephens a , Martijn Meeter a , Wouter Kruijne b
Abstract
warned reaction time task
the warning stimulus (S1) initiates a process of temporal preparation, which promotes a speeded response to the impending target stimulus (S2)
participants learn the timing of S2 by storing a [memory trace](memory trace.md) on each trial, which contains a temporal profile of the events on that trial.
On each new trial, S1 serves as a retrieval cue that implicitly and associatively activates memory traces created on earlier trials, which jointly drive temporal preparation for S2
two different S1s were associated with two different distributions of S1-S2 intervals: one with predominantly short and one with predominantly long intervals
Experiments differed regarding the S1 features that made up a pair, ranging from highly distinct (e.g., tone and flash) to more similar (e.g., red and green flash) and verbal (i.e., “short” vs “long”).
This cueing effect persisted in a subsequent transfer phase, in which the contingency between S1 and the timing of S2 was broken – a fact participants were informed of in advance
these findings support the role of S1 as an implicit retrieval cue, consistent with MTP.
A multiple trace theory of temporal preparation
In this paradigm, the researcher varies, within a block of trials, the duration of the foreperiod between a warning stimulus (S1) and a target stimulus (S2), and measures the participant’s response time (RT) with respect to S2.
as the foreperiod increases, mean RT decreases toward an asymptote (e.g., Niemi & N ̈ aat ̈ anen, ̈ 1981; Woodrow, 1914), indicating a gradual growth of temporal preparation toward a maximum
exponential (“nonageing”) distribution
frequency of consecutive foreperiods decreases according to a fixed rate
and the RT – foreperiod function has been shown to be approximately flat
MTP, which makes three main assumptions.
within-trial processing dynamics
detection of S1 prompts a preactivation of task relevant effectors, which is counteracted throughout the foreperiod by a process of continuous inhibition
Inhibition is lifted when S2 is presented, allowing activation to drive response execution
when transcranial magnetic stimulation is applied to human motor cortex, the motor evoked potential measured at the corresponding effector has been shown to be smaller during the foreperiod than at baseline, prior to S1 onset
Since this reduced activation has been found for all potential effectors in a choice reaction task, it has been argued to reflect a general mechanism of impulse control that prevents premature response
trace formation
unique [memory trace](memory trace.md) is created on each trial, which contains the temporal profile of inhibition (during the foreperiod) and activation (after S2 occurrence) experienced on that trial, along with representations of S1, S2, and the response to S2
each new [memory trace](memory trace.md) is added to an accumulating pool of memory traces created on earlier trials
these traces vary in strength
strength of each trace is maximal upon its formation and gradually reduces toward an asymptotic value as it grows older
trace expression
previously formed memory traces jointly determine the state of temporal preparation during the ongoing foreperiod
process is initiated on each trial by the presentation of S1
as the foreperiod elapses, each retrieved trace contributes to preparation in accordance with its strength and its momentary value of activation or inhibition
at each moment during the foreperiod the state of preparation is determined by the ratio of the weighted activation over inhibition values aggregated across memory traces
we assume that the state of temporal preparation reached at the moment of S2 presentation determines RT according to an inversely proportional function
This relationship can be appreciated by conceiving the state of temporal preparation as the distance of potential neural excitability relative to a fixed motor-action limit
the consecutive foreperiods occur with a ratio of 1:2:4:8, temporal preparation is very low just after the presentation of S1 in view of the low ratio of activation over inhibition across memory traces.
These dynamics thus give rise to the typically observed steep RT – foreperiod functio
In the case of an exponential distribution (Fig. 1B), where consecutive foreperiods occur with a ratio of 8:4:2:1, activation starts to dominate inhibition quickly after the presentation of S1.
Thus, preparation is already close to ceiling by the time the shortest foreperiod has elapsed and it remains at that level if the foreperiod lengthens (Fig. 1D), yielding the characteristically flat RT – foreperiod function
