Post-Cue Simulation

The ISAM solves the post-cue paradigm such that it first receives equal input by the two objects of the stimulus display. If both the activations surpass the sensitivity valueσ, the objects are said to be recognized and stored, such that their activation is persistent even after the display switches to the color cue.

If we run a simulation with the parameter values derived in the calibration phase described in section 6.2.2 on the post-cue paradigm, we encounter a problem we already know from investi-gations of the dynamics of the ISAM in a setting with varying response stimulus intervals. The adaptation of the threshold is too quick to accurately solve the task of the post-cue paradigm.

The threshold shoots over both the target and the distractor representation activation. To solve the problem, we assume a mechanism that is able to adjust the threshold behavior to the particular task demands. In the present case, the threshold is slowed by manually adjusting the following param-eters toν=0.55,γ=0.002 and∆=50. With these parameter values, the threshold stays below both relevant activations until the target color boost adds enough total activation to the system.

Note that both target and distractor activation rise similarly, separated only by their activation values right at stimulus onset, see figure 6.4. Therefore, only perceptual issues of the probe trial

6 Perception or Selection Effect

0 0.2 0.4 0.6 0.8 1 1.2

activation

10 12 14 16 18 20 22 24 26 28 30

0 0.2 0.4 0.6 0.8 1

task

time [s]

TT DT_SW TT TT_SW DT_SW CO CO_SW

Figure 6.4: Simulation run for the post-cue paradigm with the adjusted threshold parametersν= 0.55, γ=0.002 and ∆=50. The top plot shows the dynamics of representation activations in red and green and different textures for different objects and threshold θin blue. The bottom plot shows the time course of the two task evidence variables in units of ˆξ. Note that the slower adaptation ofθdoes not lead to artifacts as the attempt to respond before the cue appears.

can influence the first reaction time R^si. A detailed listing of simulated reaction times, see fig-ure 6.5, and effect strengths is given in table A.7. In summary, the ISAM predicts only slowing effects of around 40 ms in R^si for the conditions that are subject to the forced decay if a probe stimulus reappears with a different color, i.e. DT, TD, TT_SW and DD_SW. In R^ts, the above con-ditions are again slowed, TD and DD_SW weaker than DT and TT_SW. The other four concon-ditions, TT, DD, DT_SW and TD_SW, are faster than the respective control condition with TT having the strongest benefit.

6.3 Hypotheses

As already mentioned in section 6.1.3 we will mainly focus on the analysis of priming effects in the two conditions DT and TT, the classical negative and positive priming conditions. Therefore, we only give hypotheses for further conditions, if a particular hypothesis also applies to other conditions.

As denoted in section 6.2.1, the ISAM is able to generate detailed hypotheses for the current series of experiments. For the pre-cue experiment, the ISAM predicts a slow-down of about 14 ms for trials where the repeated object changes color and a speed benefit of 20–30 ms for the condi-tions TT, DD, DT_SW and TD_SW. The post-cue experiment is predicted to produce very large slowing effects of about 70–95 ms distributed equally between the two reaction times in the con-ditions with a perceptual switch, and a comparably weak positive effect of 18–27 ms which is exclusively present in the target selection phase R^ts.

6.3 Hypotheses

CO DT TT TD DD CO_SW DT_SW TT_SW TD_SW DD_SW

Reaction Time [ms] 0200400600800100012001400 CO DT TT TD DD CO_SW DT_SW TT_SW TD_SW DD_SW

Reaction Time [ms] 02004006008001000

R^si R^ts

Figure 6.5: Simulation results for the post-cue paradigm. The left plot shows both partial reaction times stacked on top of each other to point up the priming effects in the overall reac-tion times. The right plot compares both partial reacreac-tion times individually. Note the identical R^siwith perceptually identical displays. Perceptually, only a negative effect is present which has its origin in the forced decay of activation the ISAM incorporates.

Positive effects are only present in the stimulus identification phase.

Episodic retrieval as well as response retrieval theory predict a prime retrieval in all conditions apart from CO, with a tendency for a stronger memory retrieval for identically repeated objects.

As response retrieval postulates only the response to be retrieved, no effects are expected in the first part of the trial. Only the target selection phase should carry all priming effects in a way that only repeated responses benefit from retrieval, i.e. only the TT condition and a bit weaker the TT_SW condition are faster than control. All other priming conditions should trigger by their perceptual similarity a retrieval of the, in this case false, response. Thus all other conditions are expected to produce negative priming. The same effects are to be expected for the first two experiments. Traditional episodic retrieval postulates the retrieval of the entire prime episode depending on stimulus similarity. Therefore, a perceptual benefit is to be expected in every priming condition besides CO. In cases where the to-be-attended object is retrieved together with some conflicting action advice, i.e. DT, DT_SW, a counteracting deceleration in the later part of the trial is conjectured. If the action advice matches, as in TT and TT_SW trials, Episodic Retrieval makes the prediction of additional benefit.

Distractor Inhibition expects perceptual facilitation in conditions where the prime target is re-peated, and a perceptual slowing if the prime distractor is repeated. Predictions for the reaction time of the target selection phase R^tsare hard to obtain, as the dynamic system underlying

dis-6 Perception or Selection Effect

tractor inhibition theory is too complex to guess the outcome in the second phase of the post-cue experiment. Late priming effects depend on the mechanism by which objects are classified and identified, be it at a saturation level, where no priming effects could be carried over to the late phase, or at intermediate activation levels like in the simulation of the ISAM, when positive as well as negative priming can still cause behavioral effects in the later stage.