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Use of 'um' in the deceptive speech of a convicted murderer

Author(s): Arciuli, J.A. ; Mallard, D. ; Villar, G.M.

Applied Psycholinguistics

2012

33 1

83 - 95

Previous studies have demonstrated a link between language behaviours and deception; however,

questions remain about the role of specific linguistic cues, especially in real-life high-stakes lies. This study

investigated use of the so-called filler, `um¿, in externally verifiable truthful versus deceptive speech of a

convicted murderer. The data revealed significantly fewer instances of `um¿ in deceptive speech. These

results are in line with our recent study of `um¿ in laboratory elicited low-s ...

ISSN: 0142-7164

http://dx.doi.org/10.1017/S0142716411000117

http://researchoutput.csu.edu.au/R/-?func=dbin-jump-full&object_id=20219&local_base=GEN01-CSU01PL:

FT:

1

Use of ‘Um’ in the Deceptive Speech of a Convicted Murderer

Gina Villar1, 2

Joanne Arciuli1

David Mallard2

1Faculty of Health Sciences, University of Sydney, Australia

2Psychology, Charles Sturt University, Australia

Corresponding author:

Gina Villar

Faculty of Health Sciences

The University of Sydney

75 East St,

Lidcombe, 2141

NSW, Australia

Email: gvil2424@uni.sydney.edu.au

Tel: +61 024784 3081

Fax: +61 024784 3081

2

Abstract

Previous studies have demonstrated a link between language behaviours and deception;

however, questions remain about the role of specific linguistic cues, especially in real-life

high-stakes lies. This study investigated use of the so-called filler, ‘um’, in externally

verifiable truthful versus deceptive speech of a convicted murderer. The data revealed

significantly fewer instances of ‘um’ in deceptive speech. These results are in line with our

recent study of ‘um’ in laboratory elicited low-stakes lies (Arciuli, Mallard, & Villar, 2010).

Rather than constituting a filled pause or speech disfluency, ‘um’ may have a lexical status

similar to other English words and may be under the strategic control of the speaker. In an

attempt to successfully deceive, humans may alter their speech, perhaps in order to avoid

certain language behaviours that they think might give them away.

3

Use of ‘Um’ in the Deceptive Speech of a Convicted Murderer

It is widely accepted that lying produces systematic changes in behaviour, on the part of

the sender of the lie; however, people generally perform at chance or only slightly above

chance when attempting to distinguish between truthful and deceptive behaviour in others

(Bond & DePaulo, 2006). This level of performance extends to those who routinely make

veracity judgments as part of their professional role (Vrij, 2004). It seems that people have a

tendency to rely on cognitive heuristics (Levine & McCornack, 2001), overestimate

dispositional factors (O’Sullivan, 2003), overestimate nonverbal cues (Vrij, 2008) and

generally attend to incorrect cues (Akehurst, Köhnken, Vrij, & Bull, 1996; Mann, Vrij, &

Bull 2004). Therefore, research efforts have focused on identifying objectively quantifiable

cues that discriminate between truth and deception, independent of the human observer

(Zhou, Burgoon, Nunamaker, & Twitchell, 2004).

Language behaviours show great potential in this endeavour as they draw on processes

that have been associated with deception including working memory, attention, motivation

and impression management (e.g., Burgoon & Floyd, 2000; Zuckerman, DePaulo, &

Rosenthal, 1981). In the current study we focused on one language behaviour in particular,

the use of the so-called filler ‘um’ in real-life high-stakes lies. We analysed the truthful and

deceptive language of a convicted murderer, Scott Peterson, by examining speech which he

produced in two different contexts: when speaking with suspicious and unfamiliar person/s

(formal media interviews) and when speaking with a supposedly naïve but familiar person

(personal telephone conversations with a mistress, Amber Frey). This study augments our

recent study (Arciuli, Mallard, & Villar, in press) where we examined the discriminative

ability of ‘um’ in laboratory elicited low-stakes lies versus truth.

4

The Discriminative Utility of ‘Um’

As discussed by Arciuli et al. (in press) there are two possibilities regarding the

discriminative utility of ‘um’. One hypothesis predicts more frequent use of ‘um’ during

deception when compared with truthful speech. The alternative hypothesis predicts less

frequent use of ‘um’ during deceptive speech.

It has often been argued that utterances such as ‘um’, ‘ah’ and ‘mm’ constitute filled

pauses (e.g., Maclay & Osgood, 1959), or errors that produce disfluent speech (Chomsky,

1965; Goldman-Eisler, 1968). Disfluencies are ubiquitous in spoken language and although

there is substantial variation between individuals, there is evidence to suggest that up to 6%

of language may be considered disfluent (Fox Tree, 1995). It has been suggested that the

association between disfluency and deception operates via increased arousal (for instance, in

response to anxiety) and/or cognitive load that often occurs during lying (e.g., Vrij, Edward,

Roberts, & Bull, 2000). According to such a view, increased use of ‘um’ during deceptive

speech does not reflect strategic processes on the part of the deceiver per se, but is a by-

product of the increased emotional and cognitive effort associated with self-regulatory

behaviours during the construction and execution of a lie.

Alternatively, less frequent use of ‘um’ in deceptive speech might reflect a deliberate

attempt to evade detection, particularly within the framework of interpersonal

communications. Certainly, there is a folk belief that instances of ‘um’ indicate production

problems (Fox Tree, 2007) that are strongly associated with deceptive behaviour (DePaulo,

Rosenthal, Rosenkrantz, & Green, 1982; Vrij, Edward, & Bull, 2001); hence, deceivers may

seek to control their use of these utterances to improve credibility (Akehurst et al., 1996).

Central to this hypothesis is the view that liars are able to strategically monitor their

deceptive behaviours in an attempt to conceal ‘leakage’ of cues (Johnson, Henkell, Simon, &

Zhu, 2008). Of relevance here is the claim that ‘um’ may not be accurately conceptualized as

5

a speech disturbance, but rather, may have lexical status similar to other English words (Clark

& Fox Tree, 2002). Presumably, lexical status would enable a higher degree of strategic

control over the production of such utterances. It has been demonstrated that speech content

is easier to control than nonverbal behaviour during deception (DePaulo & Kirkendol, 1989).

In studies unrelated to deception, speakers can and do successfully reduce their usage of ‘um’

through conscious control (Clark & Fox Tree, 2002; Kowal et al., 1997).

The Importance of Examining ‘um’ as a Stand Alone Variable

Importantly, ‘um’ and other types of utterances such as ‘uh’ may serve divergent

communicative functions. For instance, Smith and Clark (1993) proposed that ‘um’ and ‘uh’

differ from each other in the length of the delay they signal – perhaps in order to better

inform the listener of subsequent information. Specifically, ‘um’ signals a long delay and

‘uh’ signals a short delay. Furthermore, ‘um’ tends to occur more frequently at the beginning

of a sentence and is used more often when additional delays are anticipated. Thus, despite the

common perception that ‘um’, ‘uh’ and other such utterances are interchangeable in that they

serve the same function, in reality, they may not be. In the deception literature, ‘um’ has

almost always been operationalised in combination with other utterances such as ‘uh’, ‘er’

and ‘mmh’.

The work of Kasl and Mahl (1965), in a study unrelated to deception, appears to be the

genesis for this particular taxonomy. In their study of the relationship between speech

hesitations and anxiety, Kasl and Mahl claimed that ‘um’, ‘eh’ and ‘er’ are variants of ‘ah’.

They combined these utterances to form a single variable they labelled “ah disturbances” (p.

426). In contrast, they labeled sentence changes, repetitions, stutters, tongue slips, sentence

incompletions, word omissions and incoherent sounds as “non-ah speech disturbances” (p.

430). In the deception literature there are a number of references to this particular taxonomy

and it appears to have been widely applied in the investigation of speech disfluencies and

6

pauses (e.g., Bond 2008; Bond, Kahler, & Paulicelli, 1984; DePaulo et al., 1982; DePaulo et

al., 2003; Kraut, 1978; Kraut & Poe, 1980; Riggio & Friedman, 1983; Vrij, Akehurst,

Soukara, & Bull, 2004; Vrij et al., 2000; Vrij & Mann, 2001). Consequently, the grouping of

‘ah’, ‘er’, ‘mmh’ and ‘um’ together has been routinely accepted in the deception literature,

and perpetuated from study to study. However, during the past five decades the field of

psycholinguistics has produced some important findings regarding the role of so-called fillers

such as ‘um’. As a result, some of the assumptions in the work of Kasl and Mahl may benefit

from a reappraisal in light of this contemporary knowledge. We contend that grouping ‘ah’,

‘er’, ‘mmh’ and ‘um’ together may be obscuring the discriminative ability of ‘um’ where

deceptive language is concerned.

To illustrate, consider three studies which have examined ‘um’ in real-life high-stakes

lying (Davis, Markus, Walters, Vorus, & Connors, 2005; Mann, Vrij, & Bull, 2002; Vrij &

Mann, 2001). Vrij and Mann (2001), in their study of a convicted murderer who later

confessed to the crime, found no significant difference in the frequency of what they labeled

‘uh disturbances’: “frequency of saying ‘uh’ or ‘mmm’ between words” (p. 192). It is unclear

whether ‘um’ was also included as an ‘uh disturbance’. In a subsequent study, in which Mann

et al. (2002) examined the verbal and nonverbal behaviour of 16 suspects during police

interviews, ‘um’ may have been included in a broader category labeled ‘speech disturbances’:

“frequency of saying “ah” or “mmm”, etc. between words, frequency of word and/or sentence

repetition, sentence change, sentence incompletion, stutters etc.” (p. 370). Mann et al. (2002)

found no significant differences between lying and truth telling on this variable. Similarly,

Davis et al. (2005) grouped ‘um’ with “uhs, sighs, gutturals” (p.691) under the heading of

‘non-lexical sounds’. This variable was positively associated with truthful utterances. The

authors suggested that the discriminative ability of these ‘non-lexical sounds’ may have

emerged in this study because, unlike previous studies, these sounds had been measured

7

separately from “other forms of speech disturbance” (p. 700), such as word/phrase repetition,

sentence incompletion, stutters and so on. They recommend that, in future studies, ‘um’s,

‘uh’s, sighs and gutturals be measured together as a separate variable from other speech

disturbances. We posit that ‘um’ be measured independently.

To further illustrate, consider two frequently cited meta-analyses of cues to deception

(DePaulo et al., 2003; Sporer & Schwandt, 2006). In the first of these, DePaulo et al. (2003)

examined 14 studies to conclude that the ‘fluency’ category of ‘filled pauses’ (defined as

“utterances such as 'ah’, ‘um’, ‘er’, ‘uh’, and ‘hmmm’”, p. 114) is not a reliable indicator of

deception. However, several of those studies did not specify whether ‘um’ was included in

their analysis (Bond, Kahler, & Paolicelli, 1985; Bond, Omar, Mahmoud, & Bonser, 1990;

Cody, Lee, & Chao, 1989; Hocking & Leathers, 1980; Riggio & Friedman, 1983; Vrij, 1995;

Vrij & Heaven, 1999; Vrij & Winkel, 1990). Of the remaining studies that did specify the

inclusion of ‘um’, it formed part of a composite variable with other so-called fillers such as

‘uh’, ‘er’, ‘mmh’ and occasionally with sighs, guttural sounds, false starts and the like

(DePaulo et al., 1982; Feeley & deTurck, 1998; Knapp, Hart, & Dennis, 1974; Miller,

DeTurck, & Kalbfleisch 1983; Porter & Yuille, 1996). None of the studies in this meta-

analysis included a measure of ‘um’ as a variable in its own right.

In the second meta-analysis Sporer and Schwandt (2006) examined 35 studies and

quantitatively summarised the results of 121 estimates of so-called ‘paraverbal’ cues to

deception. These cues included filled and unfilled pauses, message duration, number of

words, pitch, repetitions, response latency, speech errors and speech rate. In this meta-

analysis, ‘um’ was included in the category of ‘filled pause’, along with “speech disturbances

such as uh, er…ah, etc” (p. 424). Like DePaulo et al. (2003), Sporer and Schwandt concluded

that filled pauses are not reliable indicators of deception. However, only five of the 35 studies

(DePaulo et al. 1982; Ebesu & Miller, 1994; Knapp et al., 1974; Kraut, 1978; Vrij & Winkel,

8

1991) examined filled pauses and none of these measured ‘um’ as a variable in its own right.

Once again, effects for ‘um’ may have been obscured.

A search of the deception literature between the years of 1994 and 2009, using data-

bases from a range of disciplines including psychology, linguistics and computer sciences,

revealed that only two published studies (Arciuli et al., in press; Benus et al., 2006) have

measured ‘um’ as a variable separate from the others with which it is commonly grouped.

The findings from our laboratory based study, in addition to the findings of Benus et al.

(2006) suggest that when ‘um’ is measured independently of other variables, its increased

usage is associated with truth relative to lies. However, both of these studies examined only

low-stakes lies. Due to the practical and ethical difficulties associated with investigating real-

life high-stakes lies, very few studies have been able to provide comparative data to

demonstrate that the same patterns of behaviour are seen across a variety of types of lies.

Several authors have noted that cues to deception may be moderated by how motivated the

deceiver is to evade detection and it is possible that the indicators of deceit that are observed

in low-stakes lies will be different to those observed in high-stakes lies (e.g., Burgoon &

Floyd, 2000; DePaulo et al., 2003; Hancock, Curry, Goorha, & Woodworth, 2008).

In summary, operationalising ‘um’ in combination with other variables may obscure the

discriminative utility of this variable. The present research was designed as a companion

study for our recent investigation of the use of ‘um’ during low stakes lies, in order to further

explore the discriminative ability of ‘um’ in the real-life high-stakes lies of a convicted

murderer.

Predictions of the Current Study

As our recent research revealed significantly decreased use of ‘um’ during deception in

laboratory elicited lies (Arciuli et al., in press), we expected that ‘um’ might be observed less

frequently in Peterson’s deceptive language, although it was an open empirical question as to

9

whether patterns seen in low stakes lies would also be seen in high stakes lies. Given the

ubiquitous nature of ‘um’ in everyday language, we predicted that any discriminative utility

of ‘um’ would be apparent in both Peterson’s private telephone conversations with his

mistress (i.e., the Frey Tapes) and his media interviews.

Method

Design. It is a non-trivial task to establish ground truth in research that is conducted using

real-life high-stakes lies that were elicited outside of the laboratory. In the current study, in

order to establish which stimuli are truthful and which were not, determinations of veracity

were not based on verdict. Rather, we included only those utterances which could be firmly

established as either truth or lie by independent information.

First, it was necessary to separate the data into two sub-sets for separate analysis (Frey

Tapes and Media Interviews) because the production contexts may have differed in several

ways. For instance, it may be a more complex task to attempt to successfully evade detection

in the audio-visual modality (television interviews) compared with the audio modality alone

(taped phone calls). Specifically, on television both verbal and nonverbal behaviour is on

display. Second, it is not known whether Scott Peterson may have prepared more for the

televised interviews compared with the telephone conversations. There is some suggestion

that Peterson employed a media consultant to coach him in preparation for his public

television appearances. As a result, some of his responses may have been partially scripted or

rehearsed and, depending upon the questions Peterson anticipated being asked, this may have

impacted upon the cues to deception that were observed. Third, the target of the deception

(his mistress Amber Frey versus interviewer/millions of viewers) and the subsequent

interpersonal use of language may have differed between contexts. Lastly, the content

differed somewhat between production contexts.

10

Participant. We analysed the speech of Scott Lee Peterson, a North American Caucasian

male with no prior convictions who was arrested in April, 2003, for the murder of his

pregnant wife, Laci Peterson, who disappeared from their home in Modesto California on

Christmas Eve, 2002. Peterson was subsequently charged, convicted and sentenced to death

under the California Penal Code for the double-murder of his wife and their unborn son in

2004. Peterson was born in San Diego, California, on October 24, 1972. English is his first

language and his highest level of academic achievement is a university degree in agricultural

business. Prior to Peterson’s arrest he was employed as a fertilizer salesman.

Case Details. When Scott Peterson reported Laci Peterson missing on December 24, 2002,

the 27 year old was due to deliver her first child, to be named Conner, 6 weeks later. Peterson

was first interviewed by police on the day of Laci’s disappearance then on several further

occasions as the search for Laci continued. Search warrants had been issued on his home,

vehicles and place of business and he was under police surveillance from early January 2003.

Although Peterson told police in his first interview that he was not involved with another

woman, six days after Laci was reported missing, a woman by the name of Amber Frey

contacted police to say she had been having a romantic relationship with Peterson for several

weeks since November 19, 2002. She claimed that during that time Peterson had lied to her

about his real circumstances by presenting the guise of a recently bereaved widower living in

Sacramento, who travelled routinely for business. Frey claims she had only been told of his

real identity on the day of her contact with police, by a friend who recognised Peterson from

news reports.

Frey agreed to co-operate with police by secretly taping her telephone conversations with

Peterson from December 31 and he continued to call Frey following the disappearance of his

11

wife. During this time, Peterson repeatedly denied to police that he had been having a

relationship with a woman other than his wife, even when he was eventually confronted with

a photograph of Frey. At this point, Peterson told Frey he had lied to her about his

circumstances and confessed to her about the search for his missing pregnant wife. Their

affair became public knowledge on January 24, 2003 when Frey made a statement at a news

conference orchestrated by the police. In response to the heated public response to Peterson’s

relationship with Frey, Peterson conducted four televised media interviews from January 27 –

29, 2003 during which he was later found to have lied on at least one occasion.

On April 18, 2003, Scott Peterson was arrested by police for the murders of his wife and

unborn child following the discovery of the bodies of Laci and Connor on the shores of San

Francisco Bay on March 12. The case went to trial in June, 2004, where Peterson pled not

guilty of the charges – five months later the jury found him guilty of murder in the first

degree for his wife and murder in the second degree for his unborn son.

Materials. Transcripts of four televised media interviews in which Peterson spoke about his

wife’s disappearance (each of between 20 and 30 minutes duration), and approximately

eleven hours of taped telephone conversations between Peterson and his mistress Amber Frey

(recorded over a period of 5 weeks), all of which were admitted as evidence at trial, formed

the data for this study. Peterson did not actually testify at his own trial, so there were no

samples of testimony speech data for examination. However the trial transcript itself was still

required in the analysis for verification purposes: it was used to isolate segments in

Peterson’s speech that were subsequently identified as truth or lie at trial.

Procedure. A single person coded the data using the procedures outlined in our earlier paper

(Arciuli et al., in press). Prior to analysis of the speech data, each of the transcripts was

12

compared to the original audio of the interviews (where these were available) and telephone

conversations to ensure they were a complete and accurate record of the interviews.

Consistent with the methodology used by Vrij and Mann (2001), Mann et al. (2002) and

Davis et al. (2005), portions of each interview and telephone conversation that could be

verified as being truth or lie, were identified in the data. This involved a meticulous reading

of each of the media and wiretap transcripts to isolate any utterances that could be strongly

supported, by evidence presented at trial or from another reputable source, as either truthful

or deceptive. Deceptive utterances were identified as those samples of speech where

information was manufactured, hidden or manipulated.

Consistent with the methodology originally employed by Mann et al. (2002), fragments

were isolated so as to ensure any uncorroborated material or topic changes were excluded.

Consequently, fragments were of varying length and independent of sentence structure to

some extent. The majority of speech data available in the interviews were discarded because

there was no way of corroborating it as truth or lie. For instance, it is impossible to verify

Peterson’s thoughts or personal opinions. One example of this is when Peterson responds to a

question by the media interviewer Diane Sawyer who asked Peterson why his mistress,

Amber Frey, came forward to provide the police with information about their relationship.

Peterson responds, “It’s the appropriate thing to do. It really shows what a person of character

she is, um and it allows us to um get back to looking for Laci”. Clearly this segment must be

discarded because we cannot know whether this was Peterson’s true opinion or not.

Each sample was coded for the presence of the target variable ‘um’ using Wmatrix

(Rayson, 2008), a web-based interface tool for linguistic analysis of English text which

generates word frequency profiles from a concordance of each sample. The presence of ‘um’

in each of the four conditions was calculated as a percentage of the total number of words per

sample.

13

Results

The sample sizes of each of the four conditions (measured as the total number of words

per condition) differed: n = 180 words for the media interviews/deception condition, n = 690

for the media interviews/truth condition, n = 840 for the Frey tapes/deception condition and n

= 1,018 for the Frey tapes/truth condition. Table 1 provides examples of speech from each

condition.

-------------------------------------------------------------------------------------

Table 1

-------------------------------------------------------------------------------------

To test the discriminative utility of ‘um’, word frequency profiles were generated for each

sample and analysed using the log likelihood ratio (LR) test. LR in the present study refers to

the logarithm of the ratio between the likelihood that the truthful and deceptive speech inputs

from the participant have the same linguistic profile and the likelihood that the linguistic

profiles differ from each other. LR is less likely to overestimate significance than traditional

statistical tests such as z-ratios that rely upon assumptions of a normal distribution. Of

particular relevance to the present study, LR has the added benefit of being suitable for

comparison of texts of differing lengths (Dunning, 1993; Rayson, Berridge, & Francis, 2004).

The frequency of ‘um’ as a percentage of the total number of words in each of the four

conditions, including confidence intervals as an indication of the true range in which the

effect is likely to occur, is shown in Table 2.

-------------------------------------------------------------------------------------

Table 2

-------------------------------------------------------------------------------------

14

The critical value for LR (Λ) at an alpha of .05 was calculated at 3.84. Log linear

comparisons of the presence of ‘um’ revealed there was a significant main effect of veracity,

with lying accompanied by fewer ‘um’s (.25%) compared to during truth-telling (7.45%) (Λ

= 108.89, df = 1, p = .000). The main effect of speech production modality was not

significant, with only marginally more ‘um’s appearing during the media interviews (4.37%)

than during the Frey tapes (4.25%) (Λ = .02, df = 1, p = .89). There was no significant

interaction between veracity and speech production conditions (Λ = .10, df = 1, p = .75).

Discussion

Humans are ineffective lie detectors, thus, researchers have focused their attention on

identifying objective quantifiable cues to deception. There is a growing body of evidence

suggesting a link between language and deceptive behaviours (Newman, Pennebaker, Berry,

& Richards, 2003; Zhou et al., 2004), although questions remain regarding the nature and role

of particular linguistic cues, especially in real-life high-stakes circumstances. Here, we

analysed the use of ‘um’ in the truthful and deceptive speech of a convicted murderer in two

different production contexts (media interviews versus personal telephone conversations).

There are two possibilities regarding the use of ‘um’. One hypothesis predicts more

frequent use of ‘um’ during deceptive compared to truthful speech, possibly in response to

speech-planning problems associated with the additional emotional and/or cognitive

processing demands generated by lying (e.g., Vrij et al., 2000). The alternative hypothesis

predicts less frequent use of ‘um’ during deceptive speech, possibly because the sender

attempts to strategically plan and monitor the content of the message to prevent such

interjections (e.g., Johnson et al., 2008). The findings of the current study supported the latter

hypothesis with ‘um’ observed less frequently in deceptive compared with truthful speech.

This effect was observed in both production contexts of informal telephone conversations and

15

more formal media interviews. Overall, these results are in line with our recent study

examining low-stakes laboratory elicited lies relative to truth (Arciuli et al., in press), which

demonstrated that the increased use of ‘um’ is negatively associated with deception.

There is a folk belief that ‘um’ is a marker of uncertainty and, particularly, of

deceptive behaviour. Thus, its reduced usage during deceptive speech may indicate that the

speaker is attempting to control the frequency of ‘um’ in order to appear more credible. Data

from the present study emphasise the strategic nature of deceptive behaviour. Furthermore,

our findings suggest that rather than representing a speech error or disfluency, ‘um’ may be

more accurately viewed as a word (such as an interjection), used thoughtfully and

purposefully, and under the strategic control of the speaker. It would be valuable for future

studies to consider whether ‘um’ should indeed be (re)conceptualised as a lexical term, with

all the accompanying lexical properties of phonology, prosody, syntax, semantics and

pragmatics.

Note that the effects observed here, whilst striking from a statistical viewpoint, are

rather subtle from the perspective of the human observer. However, ‘um’ offers the key

advantage of being well-suited to automatic parsing of transcribed speech (as just like any

other word ‘um’ can be identified and counted using basic concordance systems). Thus, once

transcribed, ‘um’ can be systematically and objectively identified and tracked, for later

comparison with baseline speech samples from the same individual.

There are some limitations associated with the current study that are specific to the case

itself, and also speak to the methodological challenges implicit in research on real-life lies.

Within the media interviews, it is unclear whether there were any practice effects from

interview to interview; however there is research to suggest that contrary to commonly held

beliefs by forensic investigators, verbal cues to deception may remain fairly stable over

repeated interrogations (Granhag & Strömwall, 2002). Additionally, there are temporal issues

16

to consider in this data – the telephone conversation speech data span a four week period and

the interview data span a two day period. Lastly, it is acknowledged that a single-case design

has some disadvantages, namely, in terms of generalisability to other persons. However, the

current research is intended as a companion study for our recent laboratory study (Arciuli et

al., in press). Moreover, reporting on case studies is a long and well-accepted tradition, a

method that provides rich contextual information, which may otherwise be obscured in large

group comparison designs (Yin, 2003). Important findings have emerged in psycholinguistics

using this methodology (e.g., the seminal work of Garrard, Maloney, Hodges, & Patterson,

2005, that revealed linguistic markers of cognitive decline in dementia). Case studies such as

the present one provide the unique opportunity to investigate real-life high-stakes lies elicited

from circumstances which are ethically and practically impossible to simulate in the

laboratory.

It is well accepted that there are linguistic behaviours which mark the likelihood of

the presence of deception. The current study demonstrates in a real-world forensic context

the discriminative ability of the use of ‘um’. The results suggest that in an attempt to

successfully deceive, humans may strategically alter their linguistic behaviour. Furthermore,

these findings suggest that a (re)conceptualisation of ‘um’ as a lexical term which is under

the control of the speaker, as opposed to an unplanned speech error or filler, warrants further

investigation.

17

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Table 1. Examples of deceptive and truthful utterances in each condition

Media Interviews Frey Tapes

Truthful utterance

“They [Laci’s family] are

obviously um upset

with me about the um the

romantic um relationship

with Amber um and they

have little trust as

they’ve expressed in the

media to date um but I

believe that they’re still

looking for Laci.”

“Um well I’ll just I’ll just tell

you. Uh you haven’t been

watching the news

obviously. Um I have not

been travelling during the last

couple weeks. I have, I have

lied to you that I’ve been

travelling. The girl I’m

married to, her name is Laci.

She disappeared just before

Christmas.”

Deceptive utterance

“It was a couple of days after

Laci’s disappearance, I

telephoned her [Amber] and told

her the truth.”

“I’ll call when it’s my night

time. About nine hours

difference. I’ll take the train

late tonight from here to

Brussels. And then I’ll be in

Brussels for at least four

days.”

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Table 2. Frequency of ‘um’ as a function of veracity

Media Interviews Frey Tapes

Truth (CI) Deception (CI) Truth (CI) Deception (CI)

% of ‘um’s 5.22 (3.74,6.70) 1.11 (0.41,1.81) 3.93 (3.05,4.81) 0.12 (0.00, 0.28)

Note. CI = 95% Confidence Interval