A Psychological Model for Tinnitus
Hallam, Rachman and Hinchcliffe (1984, cited in McKenna, 2004) described a relatively radical
model for tinnitus for the time, based predominantly on brain activity rather than the traditional
cochlear-focused mechanisms (McKenna, 2004). As discussed in Section XXX, tinnitus can occur in
the absence of apparent ear pathology. This lends support to the psychological model which suggests
that tinnitus is both a psychosomatic and somatopsychic disorder, i.e. both pathways are critical in
determining the resultant level of distress experienced by the subject (McKenna, 2004). This theory is
consistent with the observation that there does not appear to be a direct correlation between the
perceived loudness of tinnitus and the ensuing negative effects experienced by the patient (Baskill and
Coles, 1999, Folmer et al., 1999).
Attention Filters
Further, the model proposes that both CNS and autonomic nervous system (ANS) activity are
involved in the manifestation of tinnitus and that it is necessary to consider attention filters, i.e. the
ability to process information from only one part of the environment to the exclusion of other parts
(McKenna, 2004). Attention filters are commonly described in the world of psychology, although an
exact definition seems to be uncertain (Coull, 1998). A quote from William James (1890) is often
employed by means of introduction: stating that “everyone knows what attention is: it is the taking
possession by the mind in clear and vivid form of one out of what seem several simultaneous objects
or trains of thought” (James, 1890 as cited in Coull, 1998). Today, attention is divided into different
sub-processes, including ‘attentional orientation’ (directing attention towards a particular stimulus)
and ‘selective’ attention (favouring one stimulus over another) (Coull, 1998) difference?. Overall
these represent useful concepts from which to consider tinnitus, since presence of tinnitus may not
always be perceived as it may not always receive constant attention (McKenna, 2004). Circumstances
that may influence the ability to appropriately filter information are likely to impact upon the
experience of tinnitus as it has been proposed that selective attention is governed by arousal level
(Coull, 1998). For example, when the attention system is overloaded during conditions of high CNS
and ANS arousal, tinnitus experience may be enhanced (McKenna, 2004). Factors such as
background noises and distractions may mask the tinnitus (Hallam et al., 1984). This model is
supported by the observation that many people who experience tinnitus do not report it to be
bothersome (Andersson et al., 2005e).
Habituation
Hallam et al. proposed that the progression of tinnitus is characterised by a process of
habituation (a decreased response to a stimulus following repeated presentations), such that as tinnitus
persists it gradually loses its ‘novelty’ to the listener (McKenna, 2004). This is a view further
supported by anecdotal reports suggesting that tinnitus is not problematic for the vast majority of
tinnitus sufferers, and that symptoms of annoyance/distress tend to taper over time (McKenna, 2004).
Delayed or failed habituation may arise when there is a high level of ANS arousal, sudden or erratic
tinnitus, altered circadian rhythm, impaired neural pathways or where tinnitus acquires emotional
significance through a learning process (Andersson et al., 2005e). Figure 1 is presented to describe
this process; the process of delayed habituation leads to increased tinnitus and associated distress,
whereas by contrast effective habituation results in no distress (Figure 1). Habituation, however, is a
controversial issue in tinnitus research, since there is a range of evidence both in favour and
potentially opposed to this model (see Section XXX).
Incapacitated habituation is proposed to occur in conjunction with inappropriate attention
filtering; since an attentional orientation focused on the tinnitus may increase arousal which will in
turn limit the attentional filter capability and hinder habituation (McKenna, 2004), providing an
unwanted feedback loop as drawn in Figure 1. This model is supported by reports advocating that
those who find tinnitus problematic (expressed by ‘complaining’) are more consistently conscious of
the tinnitus than those who do not find it bothersome, and further by subjective reports from patients
indicating that an improved tolerance is favoured by reduced stress levels (McKenna, 2004).
The attentional orientation towards tinnitus is proposed to be heightened in quiet
environments, i.e. where the signal to noise ratio is greater (McKenna, 2004), and this is likely to lead
to an increased awareness of the tinnitus, and hence may magnify any consequent distress (see figure
1). This theory would be supported by experimental evidence to show that increased distress is
experienced by tinnitus sufferers in quiet environments, as in fact has been reported (Stouffer and
Tyler, 1990). It is noteworthy, however, that the same study also stated that some individuals reported
the exact opposite trend (i.e. a noisy environment exaggerates the tinnitus effects) (Stouffer and Tyler,
1990), somewhat complicating matters, and perhaps highlighting one of the major challenges in
tinnitus research whereby the heterogeneity of tinnitus experiences between individuals is enormous.
Evidence for the Habituation Model
As described earlier, the main evidence for habituation has been summarised in numerous Reviews
(e.g. (Coles and Hallam, 1987)) as follows: (1) most people who experience tinnitus do not complain
about it, (2) it tends to become less troublesome over time, (3) there is little evidence to demonstrate a
correlation between the distress experienced and the perceived loudness (Baskill and Coles, 1999),
and (4) subjective reports from many clinics suggest that tinnitus sufferers often acquire tolerance.
However, the overall picture is not straightforward, in terms of the reliability of the habituation
model.
Evidence presented in the literature is, however, conflicting. In one example study, 528 tinnitus
patients were assessed by a self-reporting tinnitus questionnaire; 75% of patients found that tinnitus
severity did not worsen over time (consistent with habituation) (Stouffer and Tyler, 1990). However,
25% of patients did report that severity had increased since onset (Stouffer and Tyler, 1990).
Although not ascertained by the authors, these data suggest either that habituation is an inappropriate
model, or alternatively that the process of habituation may have been interrupted. Andersson et al.
reports that there is a general opinion that tinnitus becomes less troublesome over time, however, he
also states that tinnitus is frequently reported by the elderly population and that at this later stage it
found to give rise to particular irritation (Andersson et al., 2005a).
McKenna (2004) cited a study by Coles et al., found that most tinnitus subjects in their study sample
reported stable and consistent experiences of tinnitus in terms of loudness and annoyance, rather than
an increased tolerance (Coles et al., 1988). (The criteria employed to select the sample population and
measures of tinnitus assessment are not known to the present author, hence this result may be
interpreted with caution). Scott et al. found out from a study of more than 3000 tinnitus patients in
Sweden that most reported an increased perceived loudness with increasing duration of the tinnitus,
conflicting with the habituation model (Scott et al., 1989). Although, as McKenna (2004) points out,
the sample population was taken from a clinical population that actively complained of tinnitus; given
the high prevalence of tinnitus it is feasible that a large population may have been in existence for
whom an increased tolerance took place, but were excluded from the study because they did not
attend the clinic.
Overall there have been a number of studies testing the appropriateness of the habituation
model for tinnitus by reviewing tinnitus populations (e.g. (Dineen et al., 1997)), or by assessing the
physiological response to tinnitus (e.g (Carlsson and Erlandsson, 1991)). Presently it is difficult to
draw firm conclusions, since the results are frequently difficult to interpret due to: sample population
selection criteria issues, individual variability and the heterogenic properties of tinnitus, and the
difficulties of establishing an accurate outcome measure to quantify the degree of tinnitus
experienced.
In general, tinnitus research has not fully explained exactly how the tinnitus sound becomes
troublesome and ‘attention-demanding’ (Andersson et al., 2002). One example theory, however,
involves the changing-state hypothesis which claims that ‘auditory stimuli that change state are
particularly prone to affect cognitive processing’ (Andersson et al., 2002), and the changing nature of
tinnitus stimuli have been proposed to lead to increased distress (Andersson et al., 2005e).
Further Limitations
The original psychological model set forth by Hallum et al. (1984) does not provide an explicit
description of the exact cogitative behavioural processes that they propose to be associated with the
detection of tinnitus and the resultant distress; a more detailed model may facilitate the opportunity to
test the model in a more rigorous scientific fashion (McKenna, 2004). In fact, the relatively simplistic
cognitive behavioural model proposed, centred primarily on the conscious cognitive and behavioural
processes, lacks clarity and may require the consideration of additional complexities, such as the
subconscious brain processes (as described in the Neurophysiological Model section). In general,
experimental evidence available to support/disprove the model seems to be limited; research has
predominantly focused on the directly applied clinical question as to the efficacy of the model-based
treatments aimed primarily at treating the effects of tinnitus, rather than identifying, defining, and
eliminating the root cause (Baguley, 2002, McKenna, 2004). Overall, a more comprehensive and
clearly defined psychological model for tinnitus is likely to prove beneficial in terms guiding
treatments.