11.1 The ability to tell the time
Throughout previous chapters experimental studies have demonstrated that the subjective experience of time may be adversely affected after brain injury. These difficulties may depend on injury severity but can follow diffuse or more focal pathology and, it was argued in chapter 2, such deficits can produce more chronic disabling difficulties which have significant social and functional consequences. Of course, the weight o f evidence showing that disturbances in time estimation can follow severe brain injury does not mean that afflicted individuals have no concept of time, but simply that there may be quantitative or perhaps qualitative differences in their experience of time. The ability to monitor temporal passage and estimate duration is only one of many facets of the rather nebulous construct of psychological time. Another important aspect of the concept of time is utilised in the ability to tell the time or perform what will be called ‘clock reading’ tasks. Being able to tell the time involves understanding the relation between a standard form of temporal notation, such as the clock, and the broader notion o f time and temporal passage to which it corresponds. This entails a significant semantic memory component as the skill is a learned one requiring familiarity with conventional representations of time and its subdivisions. As discussed in chapter 3, section 3.4, knowledge about time has both numerical and linguistic aspects as well as specific properties attributable to the conventional manner in which time is conceived and measured. It seems plausible then to assume a priori that there is an important semantic memory contribution to the construct of psychological time.
Further support for a semantic element to this process comes from clinical observation that distortions of temporal experience and temporal reasoning may occur in the presence o f spared ability to tell the time at any given moment and to retain some tSmporal facts (for example, chapter 10). Disoriented patients may be able to read their wrist-watch or a wall-clock quite accurately, and compliance with rehabilitation regimes can be facilitated by the presence of a conspicuous timing device. Moreover, some dementing patients seem to retain knowledge about numbers and can tell the time despite gross semantic memory impairment (Hodges et al., 1992). This raises the possibility that there is something about conventional representations of time which is particularly insensitive to organic brain damage.
Despite these conjectures, the ability to tell the time has yet to be investigated systematically in clinical groups. Kartsounis and Crewes (1994) reported a transitory time-reading difficulty in a 57 year-old man with a posterior cerebral artery infarction. This patient had problems telling the time from a real or imagined clock face even though he could report the positions o f the hands accurately and could set clock hands to specific times on instruction. He also had significant visual perceptual problems and showed visuo-spatial neglect, in the light of which his poor performance on time transcoding with visual stimuli is difficult to establish as a selective deficit. However, his perceptual skills were reported to be satisfactory with non-degraded stimuli, and he showed no apparent neglect on clock-related tasks. His internal representations of clocks were also said to be adequate, given that he could describe their appearance from memory. Kartsounis and Crewes explain his impairment in terms of defective retrieval o f facts about clocks and time. Unfortunately they offer no evidence that such facts are preserved or suggest what they may constitute. The term Horologagnosia, by which the authors describe this impairment, is slightly misleading given the patient's perceptual
problems, and should be reserved for cases o f impaired knowledge about clocks in the absence of gross apperceptive disturbance. Interestingly, this patient also showed difficulties performing addition and subtraction with two-digit numbers (Kartsounis, personal communication) suggesting that he may have had concomitant numerical processing deficits. Clearly, more systematic study of the ability to tell the time is required in order to consider the extent to which this skill is self-contained (Tuokko et al.,1994).
In attempting to investigate this further an important preliminary step is to consider the adequacy of current accounts of the processes involved in being able to tell the time. The absence of any such explicit framework necessitates that some initial model is established, even if only on somewhat intuitive grounds. This will then permit more systematic investigation of the components of the model. On this basis a provisional framework is proposed for characterising cognitive processes involved in telling the time. First, it is assumed that digital/analogue clock reading and time production requires the integrity of basic visual and numerical skills, in addition to adequate working memory and motor functions. It may also be presumed that analogue and digital forms of time representation differ in their dependence on particular general-purpose cognitive processes (eg. perceptual skills) while sharing specific temporal properties in so far as they are associated with an abstract concept of time. Thus it is proposed that telling the time is an intermediate-level process incorporating abstract semantic representation of time and modular cognitive skills (number processing, calculation, perception etc.). This provisional model is illustrated in figure 11.1 below.
Following the same approach taken in previous chapters, the principal method of addressing this issue here is to relate time-telling performance to the status of other skills which it might be presumed to entail. Intuitively one would expect that telling the time
involved visual and numerical abilities (both of which were compromised in Kartsounis and Crewes' patient) as well as some more abstract semantic representation of time. It follows that time-telling can be considered a separable process to the extent that it may be impaired in the absence of dysfunction in other cognitive domains. Conversely, preservation of the ability to tell the time in the context of other deficits (perceptual, numerical, semantic) suggests that it is not wholly subsumed by the processes noted to be impaired.
Visual presentation Auditory presentation
r ANALOGUE TIME REPRESENTATION DIGITAL TIME REPRESENTATION ABSTRACT CONCEPT OF TIME
Written production Spoken production
Figure 11.1. Schematic model of processes involved in telling the time.
Clock time may be understood in digital or analogue form, each o f which can operate independently o f the other. The skills o f analogue time reading is generally acquired much earlier. These processes depend equally on adequate sensory functioning but differ in terms o f their numerical and visuo-spatial demands. Comprehension and production o f spoken times assumes adequate auditory-verbal short-term memory and
speech production skills. Written digital or analogue time comprehension/production requires visuo-spatial and grapheme-motor functions. Number processing abilities are essential but not sufficient for all forms o f time processing. In adults both time formats are associated with an abstract concept o f time although this may not be necessary to the task o f clock reading.