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The role of executive functions in subjective time experience is a vastly neglected area of research in the psychology of time. This is principally because most o f the cognitive studies o f time are traditional laboratory-based experiments which are not designed to utilise executive skills, while the literature on executive abilities has generally considered time as an independent variable, not a subject of study in itself. Yet, given our increasing appreciation of executive contributions to memory and especially to attention (Baddeley & Weiskrantz, 1993) there would seem to be fruitful grounds for exploring this aspect o f psychological time. Moreover, if subjective time experience is an adaptive capability, allowing individuals to regulate their behaviour according to contingencies in the environment, then the study of executive aspects of psychological time would seem to be of particular relevance.

As far as some of the more purely experimental studies are concerned, one has to raise questions about their ecological validity in so far as they are likely to be sensitive to executive aspects of psychological time. For instance, they have been justly criticised on the grounds of the artificial nature of many of the stimuli employed (Fraisse, 1984). Despite this weakness many recent experimental investigations seem to produce results that are broadly in keeping with older literatures on organisational and ergonomic aspects of temporal behaviour, the latter perhaps being more sensitive to executive functioning as they are less constrained by the demands of experimental rigour. For example, Schiffman & Greist-Bousquet’s (1992) demonstration that task interruptions are

associated with increased perceived duration is entirely consistent with Harton’s (1942) ergonomic demonstration that subjects lengthen their estimates of duration when an interval is spent doing several tasks rather than pursuing a single goal. Unfortunately, few investigators appear to be interested in risking their experimentally-obtained results by testing their generalisability within a much broader frame o f reference. One o f the most notable exceptions has been the research conducted by Boltz (1985) and her colleagues, from which they developed the Expectancy/contrast model (see section 2.4 (i) above).

There is one additional aspect of the psychological study of time however, which reflects the significance of a facet which may be subsumed under the term executive functioning. This concerns the relevance of subjective utilities in behavioural control. On the basis of the preceding discussions about the nature of subjective duration, it seems plausible that the importance of subjective utilities or goals in behavioural regulation is likely to have significant influence on how time is experienced. There is supportive data from comparative studies which suggest that an internal clock times stimuli on the basis of signal value, ie. associative strength (Roberts & Holder, 1984). Given that temporal processing is at least partially an effortful endeavour, it seems highly likely that processing resources will be made available according to perceived importance (Michon & Jackson, 1984). Certainly effective time-allocation is an essential aspect of planning in effective problem solving. As an illustration of this, Buehler et al., (1994) demonstrated in a sample of 465 undergraduates that poor planning arises because self-allocated time for task completion tends to be based on expectancy rather than past experience.

Despite the argument that executive skills may have a crucial role in psychological time (in the way behaviour is generally guided by time constraints in everyday life), there is little explicit recognition of this in models of psychological time. In this context, one particular theoretical contribution stands out as having potential for exploring the role of executive functions for time experience. Zakay (1992) has proposed that the importance assigned to time in a specific problem solving situation (which he termed ‘temporal

relevance’) affects the tolerable degree of ambiguity associated with an event’s duration (known as ‘temporal uncertainty’). In this context, temporal relevance is the subjective utility attached to time in a specific state requiring optimal adaptation to the environment, and as such “is a dynamic parameter whose level is under continuous change,” (Zakay (1992) pg.llO). Temporal uncertainty is a level of subjective predictability based on past experience, prior knowledge and anticipation.

The idea that the importance of time constraints varies across tasks is one which experimental studies have long been demonstrating without necessarily appreciating the broader relevance of this observation. Thus retrospective time estimation studies generally yield shorter estimates of subjective duration than do prospective judgements, simply because in the former paradigm subjects are not pre-wamed about the need to attend to time. In other words, the relevance of time to the task at hand is negated.

Since Zakay proposed his notion of temporal relevance there have been no attempts to specify more precisely the parameters within which the hypothesised subjective utilities operate. Still, preliminary experiments suggested that the concept could have significant clinical relevance as they demonstrated that longer prospective estimates (implying greater attention to time) occurred under conditions of greater temporal relevance. This is the essence of efficient, successful problem solving - avoid rurming out of time.

Summary

Despite the pre-eminence of the internal clock concept for much of the history of research into psychological time, there is now considerable evidence that the experience of time is not modulated by an automaton clock. The diversity and richness of human temporal experience points at least to very significant mediating contributions from attention and memory. In addition, increasing recognition within the mainstream cognitive arena of the executive modulation of some attentional and memory systems suggests that executive functions should play an important role in time experience in everyday life. To some extent this has been anticipated by theorists who have argued that

psychological time is critically influenced by ‘top-down’ influences such as prior belief and mental set (Boltz, 1985) and the importance o f subjective utilities and the perceived relevance of time (Zakay, 1992).

Attempts have periodically been made to reconcile the results of cognitive studies of time with an internal clock position (Thomas & Cantor, 1975; Glicksohn et a l, 1992; Block & Zakay, 1996). This has entailed that temporal information is effortfully encoded (Yntema & Trask, 1963), a notion which itself has been criticised (Tzeng,1979). However, the main evidence that temporal information is automatically encoded comes from studies of temporal order (Hasher & Zacks,1979) rather than of experienced duration. Thus there are grounds for considering the role of effortful processing of temporal information within internal clock frameworks as well as from cognitive perspectives. The different approaches of investigators have contributed to the confusions; memory researchers have tended to emphasise automaticity whereas psychologists studying time have argued for effortful processing.

Support for proponents of the modified internal clock has been received from animal studies suggesting, for example, that attention can influence the accumulation of pulses from an internal clock (Meek, 1984). However, as internal clock models increasingly incorporate cognitive constructs - witness the notion of a ‘cognitive timer’ used by Glicksohn et al.,(1992) and Zakay (1993b) - it becomes less appropriate to simply see them as two dichotomous classes of theories of psychological time. Instead they may function as different levels of description, applicable to different kinds of phenomena. Internal clocks are generally proposed as / descriptions of timing, usually of fairly simple actions, and are not identified with introspection. Nevertheless a fundamental difference between the approaches remains concerning the status of a complex specialised timing system, the more accurate description of which now sees internal clock theorists making use o f cognitive terminology. In contrast, cognitive theorists seek to explain and predict time experience by appeal to existing information processing systems.

In the following chapters the nature of subjective time disturbances after brain injury will be explored with particular emphasis on the role of attention, memory and executive skills. Where appropriate, attention will be drawn to the explanatory adequacy of cognitive and internal clock accounts. This will be preceded however by an account of the problems of time organisation in clinical populations which will provide the foundation for the empirical investigations which follow in subsequent chapters.

Chapter 3