Teresa Birngruber

Automatic and controlled stimulus processing in conflict tasks: Superimposed diffusion processes and delta functions.

An elaborated diffusion process model (a Diffusion Model for Conflict Tasks, DMC) is introduced that combines conceptual features of standard diffusion models with the notion of controlled and automatic processes. DMC can account for a variety of distributional properties of reaction time (RT) in conflict tasks (e.g., Eriksen flanker, Simon, Stroop). Specifically, DMC is compatible with all observed shapes of delta functions, including negative-going delta functions that are particularly challenging for the class of standard diffusion models. Basically, DMC assumes that the activations of controlled and automatic processes superimpose to trigger a response. Monte Carlo simulations demonstrate that the unfolding of automatic activation in time largely determines the shape of delta functions. Furthermore, the predictions of DMC are consistent with other phenomena observed in conflict tasks such as error rate patterns. In addition, DMC was successfully fitted to experimental data of the standard Eriksen flanker and the Simon task. Thus, the present paper reconciles the prominent and successful class of diffusion models with the empirical finding of negative-going delta functions.

Motor execution affects action prediction

Previous studies provided evidence of the claim that the prediction of occluded action involves real-time simulation. We report two experiments that aimed to study how real-time simulation is affected by simultaneous action execution under conditions of full, partial or no overlap between observed and executed actions. This overlap was analysed by comparing the body sides and the movement kinematics involved in the observed and the executed action. While performing actions, participants observed point-light (PL) actions that were interrupted by an occluder, followed by a test pose. The task was to judge whether the test pose depicted a continuation of the occluded action in the same depth angle. Using a paradigm proposed by Graf et al., we independently manipulated the duration of the occluder and the temporal advance of the test pose relative to occlusion onset (occluder time and pose time, respectively). This paradigm allows the assessment of real-time simulation, based on prediction performance across different occluder time/pose time combinations (i.e., improved task performance with decreasing time distance between occluder time and pose time is taken to reflect real-time simulation). The PL actor could be perceived as from the front or back, as indicated by task instructions. In Experiment 1 (front view instructions), evidence of action simulation was obtained for partial overlap (i.e., observed and performed action corresponded either in body side or movement kinematics), but not for full or no overlap conditions. The same pattern was obtained in Experiment 2 (back view instructions), ruling out a spatial compatibility explanation for the real-time pattern observed. Our results suggest that motor processes affect action prediction and real-time simulation. The strength of their impact varies as a function of the overlap between observed and executed actions.

Duration perception of visual and auditory oddball stimuli: Does judgment task modulate the temporal oddball effect?

The duration of rare stimuli (oddballs) presented within a stream of homogenous standards tends to be overestimated. This temporal oddball effect (OE) has been attributed to perceptual processes. The OE is usually assessed with a comparative judgment task. It has been argued, however, that this task is prone to decision biases. The present experiments employed comparative and equality judgments, since it has been suggested that equality judgments are less vulnerable to such biases. Experiments 1a and 1b used visual stimuli, and Experiment 2 auditory stimuli. The results provide no strong evidence for decision biases influencing the OE. In addition, computational modeling clearly suggests that the equality judgment is not particularly suited to distinguish between perceptual and decisional effects. Taken together, the pattern of the present results is most consistent with a perceptual origin of the OE.

The influence of stimulus repetition on duration judgments with simple stimuli.

Two experiments investigated the effects of stimulus repetition vs. stimulus novelty on perceived duration. In a reminder task, a standard and a comparison stimulus were presented consecutively in each trial, and the comparison was either a repetition of the standard or a different stimulus. Pseudowords (Experiment 1) or strings of consonants (Experiment 2) were used as stimuli and the inter-stimulus interval (ISI) between the standard and the comparison was either constant or variable. Participants were asked to judge whether the comparison was shorter or longer than the standard. In both experiments, we observed shorter judged durations for repeated than for novel comparisons whereas the manipulation of the ISI had no pronounced effects on duration judgments. The finding of shorter duration judgments for repeated as compared to novel nonwords replicates the results of a previous study (Matthews, 2011) which employed highly complex stimulus material. The present study shows that changes of simple, semantically meaningless stimuli are sufficient to result in a shorter perceived duration of repeated as compared to novel stimuli.

Corrigendum to Automatic and controlled stimulus processing in conflict tasks: Superimposed diffusion processes and delta functions [Cogn. Psychol. 78 (2015) 148–174]

Ulrich et al. (2015) proposed the Diffusion Model for Conflict Tasks (DMC). In their article, the diffusion parameter, r, was treated as an extra parameter in fitting DMC to reaction time data. However, this parameter can be regarded as a non-negative scaling parameter and thus can be kept constant during parameter estimation, for example, r = 4 msec. Fixating rwill not affect the goodness of model fits. We thank Craig Hedge, Ronald Hübner, and Mathieu Servant for drawing our attention to this point. An analytical argument clarifies this issue. Let {X(t), tP 0} be an observed random path of a Wiener process with a time-dependent drift. This process is defined as XðtÞ 1⁄4 r BðtÞ þ lðtÞ ð1Þ

Stimulus expectation prolongs rather than shortens perceived duration: Evidence from self-generated expectations.

Previous studies have suggested that unexpected stimuli are perceived as being longer than expected ones (e.g., the temporal oddball effect). These studies manipulated stimulus expectation mostly via stimulus repetitions and stimulus probabilities. However, these manipulations might affect duration judgments not only through the modulation of stimulus expectation. Therefore, the present study introduces a novel paradigm to isolate the effect of stimulus expectation on perceived duration from repetition and probability effects. In 2 experiments, participants vocalized which of 2 possible stimuli they expected in each trial immediately before stimulus presentation (self-generated expectations). Following stimulus presentation, participants performed a temporal bisection task on the duration of the presented stimuli. For both color (Experiment 1) and shape stimuli (Experiment 2), longer perceived durations were observed when stimulus expectations were fulfilled rather than violated. These results contrast with previous studies from which it has been concluded that stimulus expectation shortens perceived duration. Instead, the findings are rather in line with the idea that higher level stimulus expectation enhances stimulus processing and thus prolongs subjective duration (Matthews & Gheorghiu, 2016). Importantly, this also challenges the assumption that higher level stimulus expectation is a key mechanism driving the temporal oddball effect.

Perceived duration increases not only with physical, but also with implicit size.

When people judge the duration of stimuli, judgments are influenced by the physical size of these stimuli. Specifically, people tend to judge the duration of large stimuli longer than the duration of small stimuli. However, some authors (Bottini & Casasanto, 2010; Ma, Yang, & Zhang, 2012) have reported that even implicit size can affect duration estimates. The present study extends the results of these studies. Specifically, we examined whether the imagined size of objects would also influence duration estimates. In each trial, participants reproduced the duration of an animal word. During the presentation of the word, they were asked to imagine the words referent. The animals employed in all experiments varied in size. In Experiment 1, participants were instructed to imagine the animals in a fixed context. Reproduced duration increased not only with the numbers of letters of the animal word (i.e., physical size) but also with the size of the words referent (i.e., implicit size of the animal). Experiments 2 and 3 examined whether the effect of size would increase when the size of the animals was made more salient. The results of all experiments showed that reproduced duration increases with implicit stimulus size. In addition, Experiments 2 and 3 provide some evidence that the imagined size effect becomes more pronounced when the participants attention is drawn to the size differences among the imagined animals. It is argued that the implicit size effect is mediated by mental imagery that operates on pre-existing space–time associations.