The first approach in mental chronometry emphasizes that information pro-cessing can be divided into separate stages which are characterized by distinct cognitive operations (e.g., Donders, 1868/1969; McClelland, 1979; J. Miller, 1982; Sternberg, 1969)—such as perceptual processing, response selection, and motor processes—and focuses on response times to study these stages.
The general idea is that response times reflect the overall duration of pass-ing all stages, that is, of completpass-ing the correspondpass-ing cognitive operations.
Under this assumption, information processing can be investigated by analyz-ing the additive and interactive effects of various manipulations on response times, as this will reveal the stage(s) at which these manipulation affect information processing.
In the present research, the manipulation of interest is if-then planning.
Based on past research demonstrating that if-then planning allows people to more readily detect and attend to the stimulus specified in the if-part (e.g., Aarts et al., 1999; Achtziger et al., 2012; Webb & Sheeran, 2007; Wieber
& Sassenberg, 2006), in the first research paper we hypothesized that if-then planning enhances perceptual information processing, as indicated by a shorter perceptual stage. We tested this hypothesis in three experiments.
Strategic Regulation of Information Processing 5 Experiments 1a, 1b, and 2: PRP paradigm
The psychological refractory period (PRP) paradigm. The first two experiments draw upon a psychological refractory period (PRP) paradigm (Pashler, 1994; Telford, 1931), in which people respond to two successive stimuli S1 and S2 with responses R1 and R2, respectively. It is commonly observed that reducing the interval between presenting the two stimuli (i.e., shortening the stimulus onset asynchrony [SOA]) slows down the response to S2, whereas responses to S1 are barely affected by variations in SOA.
A widely accepted account for this PRP effect is the central bottleneck model (Pashler, 1994; Welford, 1952), which subdivides information process-ing into three consecutive stages: (1) a pre-central, perceptual stage, (2) a central stage of response selection, and (3) a post-central, motor stage.
Crucially, response selection is assumed to constitute a central bottleneck because only one central stage can be processed at any time. In contrast, pre- and post-central stages can be processed in parallel with all other stages.
How can the central bottleneck model explain the PRP effect? With short SOAs, perceptually processing S2 is already completed while S1 still occupies the central processing stage. Accordingly, central processing of S2 will be postponed until S1 releases the central stage, resulting in a cognitive slack that is reflected in a slower response to S2. With longer SOAs, the cognitive slack becomes shorter and eventually disappears, zeroing out the PRP effect.
The locus of slack logic. Importantly, this reasoning can be used to test hypotheses about the perceptual effects of experimental manipulations, such as making if-then plans. Assume that the manipulation of interest af-fects the perception of S2 (i.e., it changes the duration of the pre-central, perceptual stage of processing). With short SOAs, the manipulation effects are masked by the cognitive slack because centrally processing S2 cannot commence until S1 releases the central stage, thwarting the translation of perceptual differences between manipulations into the overall response time.
With longer SOAs, in contrast, the slack disappears and differences in per-ceptual processing are reflected by faster responses to S2. Thislocus-of-slack logic (Schweickert, 1978) implies an underadditive interaction effect of the manipulation and SOA: the manipulation effect is weaker at short compared to long SOAs. Such an underadditive interaction effect has indeed been reported for several manipulations affecting perceptual performance (e.g., stimulus intensity).
6 Synopsis The effects of if-then planning on perceptual processing. According to the locus-of-slack logic, our hypothesis that if-then planning enhances perceptual processing requires an underaddititive interaction effect of if-then planning and SOA. We tested this prediction in the first two experiments by comparing response times to S2s that were linked to a specific response in an if-then statement (forced-choice task) with S2s that were not linked to a specific response (i.e., a free-choice task). Across both experiments, we observed the predicted underadditive interaction effect of oif-then planning and SOA. Specifically, participants responded faster to S2s in the forced-choice (if-then planning) compared to the free-forced-choice task at long SOAs, whereas no such difference evinced at short SOAs.
Experiment 3: Additive-factors paradigm
The additive-factors paradigm. Experiment 3 corroborated the results of the PRP experiments using anadditive-factors paradigm (Sternberg, 1969).
Whereas PRP studies vary the SOA between two successive tasks to local-ize the effects of a manipulation on information processing, additive-factors paradigms combine two manipulations in a single task and focus on their ad-ditive versus interactive effects on response times. While an adad-ditive effect is taken to indicate that the two manipulations affect different stages of in-formation processing, an interactive effect suggests that both manipulations operate at the same stage.
The effects of if-then planning on perceptual processing. Following this logic, we manipulated stimulus brightness—which has well-documented effects on perceptual processing—and also varied whether responses to stim-uli were specified in if-then plans (forced-choice) or not (free choice) prior to a color identification task. Assuming that if-then planning enhances percep-tual processing, we expected an interaction effect of stimulus brightness and if-then planning. Our data confirmed this prediction. Responses were faster in the forced- compared to the free-choice tasks when the stimuli were bright, but no such difference evinced for dark stimuli, giving rise to a significant interaction effect of stimulus brightness and task type.
Conclusion
Across three experiments, Research Paper I demonstrates that if-then plan-ning enhances perceptual information processing. Participants responded faster to stimuli when they planned how to respond to these stimuli (forced-choice task) rather than making no such plans (free-(forced-choice task). This finding
Strategic Regulation of Information Processing 7 complements and advances prior research on the attentional consequences of making if-then plans (Achtziger et al., 2012; Wieber & Sassenberg, 2006) and supports the hypothesis that people are generally able to regulate their information processing in a strategic manner.
However, this first research paper focused exclusively on early percep-tual processing, as none of the experiments explicitly checked under which circumstances if-then planning might have additional effects on information processing, such as response selection (i.e., the central processing stage). This might, however, well be the case, in particular when the task becomes more complex and, for instance, response selection requires attentional selectivity in addition to perceptual processing. To overcome this limitation, Research Paper II studied a perceptual task that allowed to manipulate the degree of response conflict, thus varying the importance of attentional selectivity for response selection, and it turned to the second branch of mental chronometry previously mentioned.