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time\'s arrow and pupillary response Time’s arrow and pupillary response ANTJE NUTHMANN and ELKE VAN DER MEER Department of Psychology, Humboldt University at Berlin, Berlin, Germany Abstract The psychological arrow of time refers to our experience of the forward temporal progression of all n...

time\'s arrow and pupillary response
Time’s arrow and pupillary response ANTJE NUTHMANN and ELKE VAN DER MEER Department of Psychology, Humboldt University at Berlin, Berlin, Germany Abstract The psychological arrow of time refers to our experience of the forward temporal progression of all natural processes. To investigate whether and how time’s arrow is mentally coded in individual everyday events, a relatedness judgment task was used. The items each consisted of a verb (probe) and an adjective or participle (target). The temporal orientation between probe and target was varied either corresponding to the chronological orientation (e.g., shrink- ingFsmall) or corresponding to the reverse orientation (e.g., shrinkingFlarge). Reaction times, error rates, and pupillary responses were recorded. Chronological items were processed faster than reverse items. These findings suggest that time’s arrow is mentally coded in single everyday events. Pupil dilation and results of principal component analyses suggest top-down influences in the processing of temporally related items. Descriptors: Temporal orientation, Events, Pupillary response, Cognitive load The phrase ‘‘time’s arrow’’ was first introduced by Sir Arthur Eddington (1928) in ‘‘Gifford Lectures’’ to describe the irre- versible increase of entropy in isolated systems. ‘‘An arrow of time is a physical process or phenomenon that has (or, at least seems to have) a definite direction in time’’ (Savitt, 1995, p. 1). Penrose (1979) was concerned with seven possible ‘‘arrows,’’ in- cluding the process of measurement in quantum mechanics, along with its attendant ‘‘collapse of the wave function.’’ the expansion of the universe, and the direction of psychological time. The latter alludes to our experience of the relentless forward temporal progression of all natural processes. Surprisingly, in the microscopic world of atomic particles laws of nature seem to make no difference between forward and backward direction. That is, time’s arrow is not found in the basic equations of physics, but only in boundary and initial conditions that are open to explanation (Vollmer, 1985). Therefore, complex questions regarding the nature of time’s arrows must be addressed. Sklar (1995) argues in favor of time symmetry at the microlevel, time asymmetry at themacrolevel, and no fully compelling connection between the two. The present study investigates the macrolevel, namely the psychological arrow of time. In everyday experience, most event sequences are organized unidirectionally. For example, we can witness the aging of a friend and his death, but we cannot ex- perience this in the reverse order. Friedman (2002) provided ev- idence that even 8-month-old children are highly sensitive to temporal directionality in gravity-related events. These examples point to the existence of a psychological arrow of time, that is, a sensitivity to temporal directionality in real-life events. It is characteristic for event sequences and events, about which we have background knowledge, that they typically have causal relations of some sort (cf. van der Meer, 2003). Trabasso, van den Broek, and Suh (1989) differentiated, for example, mo- tivational, physical, psychological, and enabling relations. Riedl (1992) assumed that evolution structured our cognitive system to reflect all environmental events as causally related. Classical conditioning, for example, is based on animals’ and humans’ disposition to interpret events as causally related, if there is a temporal relationship between them. Most physicists and phi- losophers agree that there is a hierarchy of causality conditions. ‘‘The basic presupposition of the causality hierarchy is that of temporal orientability’’ (Earman, 1995, p. 274). That is, causality acts toward the future only. This widely accepted approach ex- plains causality by means of time’s arrow. Alternatively, one could explain time’s arrow by means of causality as proposed by Reichenbach (1956) and Gru¨nbaum (1973). They proposed that time’s arrows trace back to a causal arrow. In doing so, the asymmetrical causal relation would be required as an undefined basic concept. However, it remains completely open how events might be identified as either causes or consequences independ- ently from time’s arrows (cf. Vollmer, 1985). The present article will consider the property of temporal ori- entability or directionality as a basic presupposition of causality. According to Friedman (2002), there are at present very limited insights into the psychological processes underlying the sensitiv- ity of humans to temporal directionality in real-life events. A question that is fundamental to ask is: Is the psychological arrow of time mentally coded? Freyd’s (1987, 1992) theory of dynamic mental representations provides a general theoretical framework. She assumes the temporal dimension to be inextricably embed- ded in the mental representation of the external world and to be directional. Similarly, Barsalou (1999) argues that our mental representations of events are not arbitrary, but do preserve as- Antje Nuthmann is now at the University of Potsdam. Address reprint requests to: Elke van der Meer, Department of Psy- chology, Humboldt University at Berlin, Rudower Chaussee 18, 12489 Berlin, Germany. E-mail: vdMeer@rz.hu-berlin.de. Psychophysiology, 42 (2005), 306–317. Blackwell Publishing Inc. Printed in the USA. Copyrightr 2005 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2005.00291.x 306 pects of the initial perceptual and experiential input. For routine events, there is empirical evidence for this assumption. Routines are descriptions of stereotypical, frequently encountered se- quences of events (Galambos & Rips, 1982). Several studies demonstrated the preference for the chronological order of rou- tine events compared either with the reverse order or with a ran- dom order in using a variety of different paradigms (cf., Mandler & McDonough, 1995; Nelson & Gruendel, 1986; van der Meer, Beyer, Heinze, & Badel, 2002). On the other hand, there is very limited evidence on the rep- resentation of time’s arrow within individual events (Zwaan, Madden, & Stanfield, 2001). Adopting the framework proposed by Freyd (1987, 1992) and Barsalou (1999), time’s arrow should not only be coded in mental representations as a connection be- tween events, but also in the mental representation of individual events. The event shrinking shall serve as an example. Shrinking is a temporally unidirectional event. An object is related to the event shrinking. Among others, the object is characterized by the opposing features largeFsmall. That is, the event shrinking re- fers to an object changing from large to small. This transforma- tion might imply temporal order information. This was the starting point for the present study. According to Freyd (1987, 1992), mental representations of real-life events have an inherent time component, making them dynamic representations. This internal temporal dimension is directional, like external time. Thus, items with a temporal orientation toward future time (e.g., shrinkingFsmall) are expected to be processed faster and with higher accuracy than items with a temporal orientation toward past time (e.g., shrinkingFlarge). The first aim of the present study was to test this hypothesis. A relatedness judgment task was used. Participants had to decide whether probe–target pairs were related. The probe was a verb naming an event (e.g., shrinking), whereas the target named a feature of an object re- lated to the event (e.g., small). Relatedness of probe and target was assumed when the target was a feature that correctly char- acterized the event. For related items, the temporal orientation between probe and target was varied: It could either correspond to the chronological orientation (chronological items, e.g., shrinkingFsmall) or to the reverse temporal orientation (reverse items, e.g., shrinkingFlarge). In addition, the time interval between the presentation of the probe and the presentation of the target (stimulus onset as- ynchrony, SOA) was varied: 250 ms vs. 1000 ms. Characteristic time constants for automatic spreading activationmechanisms are a mere 200–250 ms (Fischler & Goodman, 1987; Neely, 1977). If the SOA is considerably longer, strategic processes can modify results of automatic activation (Neely, 1991). A frequently used SOA that enables strategic processing is 1000 ms. In probe–target paradigms, SOA effects do not strictly argue for either automatic activation or controlled access to mental representations (cf. van der Meer et al., 2002). However, compared with priming tasks, recognition procedures provoke elaborate, semantic processing of information and are considered to be a more direct method of measuring howmemorablemental representations are (Gernsbac- her & Jescheniak, 1995). For that reason, the recognition proce- dure was used in the current experiment. Pupillometrics A second aim of the study was to support behavioral data, that is, reaction times (RTs) and error rates, with psychophysiological data. The pupillary response has proved to be a sensitive, reliable, and consistent measure of the processing load induced by a task, orFmore broadly definedFresources allocated to a task (cf. Beatty & Kahneman, 1966; Beatty & Lucero-Wagoner, 2000; Goldwater, 1972; Hess & Polt, 1964; Loewenfeld, 1993). The following rule applies: The more difficult a task is or the more complex a cognitive process is, the more the pupil dilates. Like eye movements (see Rayner, 1998), pupillary movements are a good index of moment-to-moment on-line processing activities. Different aspects of cognitive activity have been successfully in- vestigated using the pupillary response during the last decade: language processing (Hyo¨na¨, Tommola, & Alaja, 1995; Just & Carpenter, 1993), perception (Verney, Granholm, & Dionisio, 2001), memory performance (Granholm, Asarnow, Sarkin, & Dykes, 1996; van der Meer, Friedrich, Nuthmann, Stelzel, & Kuchinke, 2003), and attention (Kim, Barrett, & Heilman, 1998). For the current study, the following global hypothesis holds: Processing of reverse items consumes more resources than processing of chronological items. To test this hypothesis, peak dilation and latency to peak were determined as parameters of the pupillary response. For reverse items, these parameters were expected to have higher values than for chronological items. Principal Component Analysis (PCA) of Pupillary Responses In addition, the current study had a third, methodological aim motivated by an apparent paradox in pupillometric research (cf. Schluroff et al., 1986): On the one hand, pupillary movements are considered to be a reliable physiological index of resource consumption. On the other hand, typical measures of the pupil- lary response are comparatively unidimensional. Thus, the ques- tion arises how to compress and analyze all the information represented by a pupillary response. In event-related brain po- tentials (ERP) research, PCA in combination with analysis of variance (ANOVA) has proven to be meaningful and successful (Donchin & Heffley, 1978). The advantage of PCA for the eval- uation of pupillary responses lies in the fact that all information of the pupil data is taken into consideration rather than that of single data points. To further investigate the usefulness of PCA in pupillometric research, we subjected averaged pupillary respons- es to PCAs (cf. Granholm & Verney, 2004; Schluroff et al., 1986; Siegle, Granholm, Ingram, & Matt, 2001; Siegle, Steinhauer, & Thase, 2004; Verney,Granholm,&Marshall, 2004).We expected to identify a component reflecting the distinct processing de- mands associated with chronological and reverse items. As for the time course of the pupillary response waveform, the differ- ence in processing chronological and reverse items was expected to appear in a rather late processing stage associated with de- cision processes. Method Participants Ninety-six psychology students of Humboldt University in Ber- lin participated in the experiment. They received either course credit or DM 10 payment for their participation. All of them had German as their mother tongue. Twenty students (17 women and 3 men; mean age: 26.1 years) participated in a first pretest to generate the experimental materials and to examine their ade- quacy. Twenty students (13 women and 7 men; mean age: 24.3 years) participated in a second pretest to examine the temporal relatedness of items. Twenty students (12 women and 8 men; mean age: 26.3 years) participated in a post hoc free association Time’s arrow and pupil response 307 study to explore the association strength between probe and tar- get, which is assumed to indicate the general semantic relatedness of the experimental materials (Strube, 1984). Thirty-six students participated in the main experiment. Six participants had to be excluded from all analyses because of technical difficulties. For themain experiment, the final sample consisted of 30 students (21 women and 9 men; mean age: 24.7 years). Students could only participate in one of these studies. Stimuli and Materials In a first pretest, participants had to generate verbs that described individual events. Additionally, they were asked to produce pairs of adjectives that are highly familiar past- and future-oriented characterizations of the previously generated events (e.g., shrink- ing: largeFsmall). In total, participants generated 136 different triplets. These triplets were examined in a second pretest. Par- ticipants were presented with a verb (e.g., shrinking) describing a change in time. The verb was accompanied by a pair of adjectives or participles (e.g., largeFsmall). Participants had to rate on a 5- point scale (from 15 very bad to 55 very good) how well the word word文档格式规范word作业纸小票打印word模板word简历模板免费word简历 pair reflected the change in time. The ratingwas assumed to show how well the word pair was able to depict changes in per- sons or objects, associated with a specific event. Those triplets (individual event and feature pair) that reached a median of at least 4 on the rating scalewere selected. Next, highly emotional as well as especially short or long triplets were excluded. The re- maining triplets were believed to best represent the temporal di- rectionality of real-life events. The chronological and reverse items (i.e., related items) were constructed in the following way: For chronological items, an individual event was combined with its future-oriented feature (e.g., steamingFtender). For reverse items, an individual event was combined with its past-oriented feature (e.g., shrinkingFlarge). Because the temporal relationship is a special case of semantic relationship, we intended to control the experimental materials for global semantic relatedness, too. In a post hoc free associ- ation study, the participants were presented with the probes (e.g., shrinking) and were asked to utter the first words that came to mind. All free associations that were generated within 10 s were recorded. For every participant and every related item, four bi- nary scores (yes vs. no) were determined, scoring 1 as ‘‘yes’’ and 0 as ‘‘no’’: (1) Was the first associative response to the presented probe the targetword? (2)Was the first response aword similar to the meaning of the target (e.g., a synonym)? (3) Was the target word within the top five responses to the probe? (4) Was a word similar to the target within the first five responses? Next, for each of the four association strength measures, the proportion of par- ticipants for whom a positive response was found was calculated. Of course, the first association measure exhibits the lowest mean probe–target association frequencies (chronological items: 0.09; reverse items: 0.07) whereas the fourth shows the highest values (chronological items: 0.24; reverse items: 0.19). These free asso- ciation findings correspond with results reported in the literature (see Strube, 1984, for a complex review). For verbs, adjectives are associated with low frequency and rather late in the association sequence. For statistical analysis, we used the mean of the four association strengthmeasures as a combinedmeasure. A 2 (SOA: 250 vs. 1000 ms) � 2 (temporal orientation: chronological vs. reverse items) item ANOVA yielded no significant effects, SOA: F(1,36)5 0.180, MSE5 0.021, p5 .674, Z25 .005; temporal orientation: F(1,36)5 0.744, p5 .394, Z25 .020; SOA � temporal orientation: F(1,36)5 1.419, p5 .241, Z25 .038.1 Thus, probe–target association frequency is equal for the experimental item groups. The main experiment consisted of two item blocks, each con- taining 12 practice and 40 test items. Each item was composed of the probe (e.g., shrinking) and the target (e.g., large). Fifty per- cent of the items were related (e.g., shrinkingFlarge); the re- maining 50% of items were unrelated (e.g., shavingFfar). For related (i.e., experimental) items, the temporal orientation be- tween probe and target could either correspond to the chrono- logical order (e.g., steamingFtender), in which case the items were referred to as chronological items, or it could run against the chronological order, in which case the items were referred to as reverse items (e.g., shrinkingFlarge). The chronological and re- verse item groups were also controlled for the number of letters (for probes, mean5 8.1 letters; for targets, mean5 5.2 letters) and word frequency (for probes, mean5 16.5 occurrences/mil- lion; for targets, mean5 248.1 occurrences/million; CELEX da- tabase; Baayen, Piepenbrock, & Gulikers, 1995). The unrelated probe–target pairs (filler items) were con- structed by using the same 40 individual events as for the related items. They were combinedwith features that had occurred in the unused triplets. Thus, in the main experiment every individual event (probe) appeared twice: In one item block it was part of a related item whereas in the other item block it was part of a filler item. Because the block order was switched between participants, the word repetition was not supposed to have a confounding effect. The experiment was run in German. All examples have been translated into English. The original materials, both in German and English, may be obtained from Antje Nuthmann. Design The following independent variables were considered in the ex- periment (within subjects): SOA (250 ms and 1000 ms) and tem- poral orientation (chronological and reverse). The participants were presented half of the items with an SOA of 250 ms (Block 1) and the other half with an SOA of 1000 ms (Block 2). The block order was switched between participants, who were randomly assigned to one of the two versions. Probe and target were either related (50%) or unrelated (50%). For related items, the tem- poral orientation between probe and target was varied: either corresponding to chronological order (50%; e.g., steamingFten- der) or reverse order (50%; e.g., shrinkingFlarge). Unrelated items (i.e., filler items) had no meaningful relation (neither tem- poral order nor global semantic relation) between probe and target (e.g., shavingFfar). These filler items were included in the experiment so that participants would not only be exposed to related items. No hypotheses weremade regarding the processing of filler items. Still, they were included in some exploratory analyses. Within an SOA condition, items were presented ran- domly. The following dependent variables were recorded: RTs, error rates, and pupillary responses. Procedure The experiment took place in a quiet, medium-illuminated room (background luminance5 500 lux). The participants received written instructions. They were seated comfortably i
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