William Stern on the "psychical time of presence". Historical and theoretical study of a cognitive model of time perception and autonoetic consciousness

David Romand
[Journal für Philosophie & Psychiatrie, Juli 2011, Supplement]

5. Conclusion: Posterity and relevancy of the theory of the psychical time of presence in current cognitive psychology and neurosciences

5.1. A decisive theoretical contribution

The aim of this paper was to rehabilitate the theory of the "psychical time of presence", a cognitive model of time perception elaborated by the German psychologist William Stern at the end of the 19th century. I tried to highlight both the historical significance and the intrinsic scientific value of Stern's contribution, while insisting on the importance it may have for contemporary research in cognitive psychology and neuroscience. This theory is based on the assumption that the experienced present, i.e., actual conscious experience, has some duration and results from the manifestation of a temporally-extended psychical phenomenon. Stern terms "psychical time of presence" the specific act of consciousness by which we are supposed to apprehend (i.e., to become aware of) mental contents that flow in consciousness during some interval of time. In contrast to the mainstream conception of time perception in the 19th century, but in accordance with the holistic trends of German psychology of his time, Stern considers that the succession of conscious phenomena is experienced directly and spontaneously. According to this view, perception of the temporal extensiveness does not consist in a process of reconstruction of time relationships: it simply results from the fact that mental contents follow up each other through the time of presence and does not require the mediation of any other psychical entity. In other words, the flow of psychical phenomena in consciousness must be regarded as experienced intuitively. For Stern, the time of presence is an elementary cognitive property of an extensive nature which ensures the unity of conscious experience and defines the basic structure of the stream of consciousness. Each manifestation of the time of presence results in the apprehension of a definite episode of conscious life. Despite a number of difficulties and inaccuracies that we have examined in detail, the theory of the psychical time of presence appears to be the most consistent model of time perception, and in fact probably the only one likely to explain our capacity of experiencing the succession of mental contents and the origin of our representation of extensiveness. More generally speaking, it brings a particularly satisfying solution to the issue of the immediate continuity of conscious experience. On the basis of a relatively simple theoretical scheme Stern succeeds in building a cognitive model endowed with a remarkable explanatory power.

Considered as a whole, the theory of the time of presence does not only account for experience of temporal extensiveness, but also for the other significant aspects of time perception, namely, perception of past and future, date, and duration. Stern's 1897 paper lays actually the foundations of a general theory of time perception and stream of consciousness. The segment of psychical life defined by the time of presence, i.e., the episode, constitutes the basic experiential and structural pattern of consciousness. This is the cognitive unit from which all other forms of conscious experience are built. The content of the time of presence per se is spontaneously experienced as being "present": it is not only an actual episode of conscious life, but an episode that is experienced as existing actually. Stern's great merit is to have understood that experience of non-actual moments of conscious life, i.e., past and future episodes, is itself an actual experience mediated by the time of presence, and thus can be interpreted on the basis of his model of time perception. Past and future events, Stern emphasizes, cannot be perceived directly but only insofar as they are reconstructed in the time of presence. Moreover, if presentness is experienced intuitively, pastness and futureness are apprehended symbolically, i.e., inferred from a presently-experienced content given in the time of presence. Mental contents we experienced previously or we expect to experience are likely to be "projected" into the time of presence, that is to say, to be retrieved or re-actualized in actual experience. As such, the contents projected are spontaneously experienced as present and then totally indistinguishable from the non-projected contents encompassed in the time of presence. As a consequence, one must postulate the existence of cognitive factors capable of differentiating experientially memory images from non-retrieved images and then to make us perceive them as non-actual episodes of conscious life. Stern distinguishes (implicitly) a "quality of pastness" and a "quality of futureness" respectively. The double process of projection and differentiation of mental contents allows us, not only to re-experience and pre-experience past and future episodes, but also to confront them with the present events of conscious experience. Comparison of separated moments of conscious life through the whole formed by the time of presence is a means of ensuring the continuity of conscious experience and the unity of the self beyond the immediate perception of successiveness and extensiveness.

The idea that the contents of the time of presence can be "projected", differentiated, and compared, appears as an extremely fruitful hypothesis from the heuristic point of view. Stern's reflections on cognitive foundations of perception of past and future can be refined and applied to two others essential aspects of time experience, namely, perception of date and duration. We demonstrated above that date and duration are not, as Stern suggests, perceived intuitively, but that their apprehension results more plausibly from a complex reconstruction process in the time of presence. Perception of date and perception of duration consist basically in the awareness of the relationships that past and future episodes have to each others and to the events of actual conscious life. In order to be perceived, these temporal relationships should be reconstituted both analogically and symbolically in the time of presence: the corresponding mental contents should be retrieved in a definite order and accompanied by temporal factors whose intensity is correlative of their relative moment of appearance in the past and in the future. According to this view, perception of date and duration result from cognitive processes that do not fundamentally differ from those engaged in the perception of past and future. They simply involve more sophisticated retrieval, comparison, and differentiation mechanisms. I remarked above that there is probably no "pure" experience of pastness and futureness, and that our perception of past and future has always something to do with our capacity of determining date and duration of events. More generally speaking, our ability to re-experience past episodes, to pre-experience future possible episodes, to date them, and to estimate their duration, corresponds to all cognitive processes by which we become aware of the temporal structure of our own conscious life.

5.2. Outlines of a general model of time perception

On the basis of the cognitive model proposed by Stern, one can draw the outlines of a general theory of time experience (for a theoretical discussion of the time experience issue in current psychology and neurosciences, see: Brown, 1990; Gallistel, 1996; Glicksohn, 2001; Tulving, 2002a). The latter may be regarded as consisting in three main functional aspects, each of them corresponding to a definite stage in the elaboration of our representation of the temporality and to some level of complexity of conscious experience. According to the theoretical scheme I propose here:

1) The first and the most fundamental aspect of time experience is perception of successiveness and extensiveness. This is the capacity of intuiting during a brief moment the flow of our conscious activity, and apprehending psychical phenomena that follow up each other during this interval of time as a single temporally-extended content. Due to the manifestation of this "time of presence" or "specious present", we are able to put in relation what we experience instantaneously with what we have experienced just before and what we will experience just after, and then to confer some duration, that is to say, some existence, to our conscious experience. In other words, perception of successiveness and extensiveness endows us with the power of retaining and maintaining together the elements constitutive of our actual experience: this is the foundation of the so-called "immediate" or "primary" memory. The intuitional act of apprehension that mediates perception of successiveness and extensiveness defines what I called above an "episode", an "experiential moment", or "actual experience", that is to say, the basic structural and functional unit of consciousness.

2) The second aspect of time experience is the capacity of distinguishing experientially, present, past, and future events of conscious life, i.e., to borrow Tulving's expression, chronesthesia (Tulving, 2002a). More precisely, what I mean here by "chronesthesia" is the cognitive function by means of which past memory images (retrospective recollections) and future memory images (prospective recollections) are discriminated, both from present experiential events and from each other. If one accepts the postulate that successiveness and extensiveness are experienced intuitively, then, one should admit that the feeling of "presentness" is spontaneously given to us with the contents apprehended in the time of presence. So, it is not sufficient to retrieve past or future episodes of our conscious life, that is, to reconstitute the corresponding mental contents in actual experience, to experience them as past or future events. To be recognised as images of the past or the future, retrieved episodes must be accompanied by some mark that gives them a characteristic temporal coloration. In other words, there must be a specific cognitive factor that mediates the feeling of pastness and the feeling of futureness respectively. The model of perception of past and future I advocate here is based on the fundamental assumption that retrieval and feeling of pastness/futureness are in reality two completely distinct cognitive properties. Chronesthesia is closely related to the issue of "secondary memory", or, more exactly, to what modern cognitive psychologists and neuroscientists call "episodic memory", and results in the manifestation of what Tulving calls "autonoetic consciousness" (these issues will be discussed later). It plays an essential role in cognitive life insofar as it contributes to extend considerably the scope and the potentialities of conscious experience. It mediates the passage from a purely intuitive form of consciousness in which experience is limited to perceiving actual psychical events that occur during a short temporal interval, to a kind of consciousness differentiated in a variety of experiential forms that allows us not only to experience intuitively actual moments of conscious life but also to apprehend symbolically its non-actual moments as definite events of past or future, and then to gain a representation of the evolution of our own conscious activity through time.

3) Perception of date and duration is the last and the most elaborated aspect of time experience. Our capacity of perceiving date and our capacity of perceiving duration should not be regarded as cognitive functions fundamentally different from chronesthesia, but simply as much more complex and accurate ways of experiencing the past and the future. Ordinary conscious life does not consist simply in intuiting the present and recollecting the past and the future, but also in apprehending the temporal relationships that exist within past conscious life and those that exist within future conscious life, as well as in apprehending the relationships between past or future events and the events of present conscious life. Experiencing the date of a conscious phenomenon consists, in cognitive words, in ascribing to an episode or a sequence of episodes a given position in the stream of consciousness, that is to say, to estimate its degree of pastness/futureness relatively to other past, present or future events of conscious life. A particular aspect of date perception is perception of recency/oldness, i.e., the ability to appreciate the more or less great remoteness and proximity of memories vis-à-vis actual experience. Perception of recency and oldness is the basis of the phenomenological distinction between short-term and long-term memory. Experiencing duration consists in estimating the length of a definite segment of the stream of consciousness, i.e., in apprehending the temporal distance that separates two or more successive events of past or future conscious life. More precisely, we should compare the different degrees of pastness or futureness of episodes that have been retrieved in the order (or the reverse order) of their appearance in the past or the future. Perception of date and perception of duration should be regarded as two cognitive functions of their own, even if mental processes engaged are probably very similar in both cases. Generally speaking, they result both from the capacity of appreciating the relative pastness/futureness of memories on the basis of their particular layout in actual experience. More precisely, each of them consists in a sophisticated retrieval, differentiation, and comparison process. Experiencing date as experiencing duration supposes that a number of mental contents are retrieved in a definite order and that temporal factors are organised in a definite pattern of differential intensities, so that the cognitive elements that compose the resulting unitary content can be compared in a specific way in the time of presence. Date perception and duration perception are two complementary cognitive functions that contribute to the emergence of the highly-structured form of consciousness that characterises ordinary psychical life. Our ordinary self is endowed with the ability, as Tulving says, to "travel mentally" through the main temporal domains of conscious life and from one domain to another (the issue of mental travelling will be discussed in detail later). Differently speaking, we have not only the possibility of re-experiencing, pre-experiencing, and intuiting virtually every episode or sequence of episodes of our conscious life, but also to identify them as elements of the stream of consciousness, that is to say, to recognize them as particular manifestations of our own self through time. Conscious activity mediated by perception of date and duration determines the structure of the stream of consciousness. From the experiential point of view, it allows us to elaborate a representation of the temporal organisation of our conscious life. This third-rank consciousness has the remarkable property of being capable of apprehending reflexively its own temporal unfolding. It should be noted that like any form of conscious experience, it exists actually only during the short experiential moment defined by the time of presence.

The model of time experience I propose here as a systematisation and an extension of Stern's reflections on the time of presence lays the foundations of a general theory of the structural and functional organisation of consciousness. According to this model, conscious experience is a hierarchically-organised cognitive activity that is closely related to our capacity of perceiving different categories of temporal relationships between mental phenomena. We can distinguish three organisational levels, each of them corresponding to a particular constructional step of our time representation. The passage from one level of consciousness to another results in the differentiation of a variety of experiential forms, that is to say, in the broadening of the scope of self-awareness and the enhancement of the complexity of the temporal structure of consciousness. Experiencing successiveness and extensiveness determines actual consciousness, the moment in which one is currently aware of his/her own mental activity. By perceiving the past and the future, one becomes aware of non-actual conscious phenomena, the experiential moments of his/her own conscious life that are by definition inaccessible to any direct awareness, whereas by perceiving date and duration, one becomes aware of the relationships that non-actual phenomena have between each others and with actual conscious phenomena [18]. In this respect, the cognitive model proposed is likely to give a global solution to the double epistemological problem of the continuity and the unity of conscious experience. Regarding the continuity issue, it accounts both for immediate continuity of consciousness, i.e., perception of the flowing of mental phenomena in actual experience, and for continuity of consciousness beyond the limits of actual experience, i.e., perception of the flowing of past, present, and future experiential moments that constitute the course of our conscious life. The second type of continuity consists in a phenomenon of short-term continuity, as well as a phenomenon of long-term continuity. Short-term continuity relates to the issue of the so-called working or short-term memory, i.e., our capacity of maintaining present events of conscious life in relation to very recent episodes of past conscious life and to episodes of future conscious life we expect to experience imminently. Long-term continuity consists in establishing at any time the connection between the autobiographical aspects of one's past and future life and one's present conscious life. Similarly, my Stern-inspired model accounts for the two main aspects of unity of conscious experience, namely, the unity of actual experience and the unity of conscious life. While the first one refers to the fact of perceiving as a consistent whole the mental contents that are being currently experienced, the second one refers to one's ability to identify the various temporal instantiations of one's own consciousness through time as being constitutive of one and unique self-identity. Immediate continuity of consciousness and unity of actual experience are ensured by perception of successiveness and extensiveness, short-term and long-term continuity of consciousness as well as the unity of conscious life by chronesthesia, date and duration perception.

5.3. Stern's legacy: The theory of the time of presence in the eyes of current research on episodic memory and autonoetic consciousness

Despite its epistemological and heuristic value, the theory of the time of presence had no direct posterity. This may be explained by Stern's unwillingness to pursue his research in time psychology after 1897, and, more generally speaking, by the disappearance of theoretical psychological studies on time perception in the beginning of the 20th century. As from the 1910s and for many decades, research on time perception will consist indeed in merely experimental investigations. Time psychology studies carried out during this period are in reality nothing but the continuation and the development of the 19th century program of research on the "sense of time" (Benussi, 1913; Durup and Fessard, 1930; Rubin, 1949/1934). It is only in the late 1950s that theoretical issues related to time perception seem to regain some consideration in experimental psychology. Interestingly, one notices then a reappraisal of the 19th century theoretical debate on time experience. Some classical assumptions were reinterpreted in the light of new empirical data; in particular, evidence was brought that the experienced present is a temporally-extended psychical phenomenon and that short durations are apprehended intuitively (Fraisse, 1957/1963; Schaltenbrand, 1967; Stroud, 1967; Vicario, 1973; Michon, 1978). The theory of the time of presence was conferred retrospectively some scientific legitimacy, but Stern's contribution itself remained totally ignored. More recently, a number of philosophers of mind have tried to revisit the question of the specious present and the stream of consciousness (Flanagan, 1992; Gallagher, 1998, 2003; Dainton, 2000). The discussion roots mainly in James' rather crude formulation of the problem and completely leaves aside the yet far more elaborated model proposed by Stern. Despite some interesting contributions, as the discussion of the "overlap hypothesis" (see above), these philosophical studies did not substantially renew the scientific debate about the time of presence. They disregard most of the issues that have been tackled in this paper, and in fact, they fail to propose a consistent theory of time perception and of the temporality of conscious experience. Moreover, they can be criticized to promote an abstract conception of consciousness that remains totally beside the empirical investigations of current cognitive psychology and neurosciences.

As suggested before, the most striking confirmation of Stern's views regarding time perception and consciousness is to be found in cognitive studies carried out during the last 40 years on episodic memory. "Episodic memory" is an expression coined by Tulving to refer to the form of memory that allows us to re-experience definite moments of our conscious life or "episodes", by contrast to "semantic memory", the form of memory that allows us recognise objects or concepts independently from the spatiotemporal context in which we experienced them before (Tulving, 1972, 1983, 1985; 2002b). Episodic memory and semantic memory are associated each with the manifestation of a specific state of awareness: in the first instance the contents retrieved are perceived as having occurred in the past ("recollection" or "remembering"), whereas in the second instance they are perceived as being "familiar", i.e., as having been already encountered ("knowing"). Experimental psychologists have formalized this phenomenological distinction between experiencing the past and experiencing familiarity, and clearly demonstrated the fact that recollection and knowing correspond to two independent cognitive variables (Tulving, 1972, 1983, Mandler, 1980; Yonelinas, 1999, 2002). In accordance with these behavioural results, there is a large amount of lesion, neuroimaging, and electrophysiological studies showing that episodic memory and semantic memory are two distinct cognitive functions mediated by two different neural networks (Henson et al., 1999; Bruckner and Wheeler, 2001; Rugg et al., 2002; Yonelinas, 2002; Wheeler and Bruckner, 2004; Yonelinas et al., 2005; Daaselar et al., 2008). In his pioneering theoretical studies on episodic memory, Tulving conceived past awareness as the expression of a more general cognitive activity termed "autonoetic consciousness", i.e., "the kind of consciousness that mediates an individual's awareness of his or her existence and identity in subjective time extending from the personal past through the present to the personal future" (Tulving, 1985, p. 1). In other words, Tulving suggested the existence of a future episodic memory as a logical functional and experiential complement of past episodic memory.

This assumption has been strikingly demonstrated by a series of recent neuroimaging studies that revealed that our ability to envision future possible episodes correlates with almost the same cerebral activation pattern as our ability to re-experience past episodes (Okuda et al., 1998, 2003; Buckner and Carroll, 2006; Addis et al., 2007; Szpunar et al., 2007). Moreover, the retrieval mechanism and the self-referential processing engaged, as well as the nature of sensory contents retrieved, were shown to be very similar in both cases (Atance et O'Neill, 2001; Addis et al., 2007; Addis and Schacter, 2008; Szpunar and McDermott, 2008; Schacter and Addis, 2009; Schacter et al., in press). Re-experiencing the past and pre-experiencing the future are now clearly proved to consist in the same cognitive capacity of reconstituting non-actual moments of conscious life in actual experience. Both forms of memory are in reality nothing but the manifestation of one and unique "episodic thinking" by which we explore mentally our own conscious life both retrospectively and prospectively (Tulving, 2002b; Addis et al., 2007; Schacter et al., in press). If there is basically no difference between retrieving past and future memory images, then the difference between retrospective and prospective memory cannot lie but in the very fact of experiencing the past and the future. In other words, there must be something like a feeling of pastness and a feeling of futureness, two cognitive properties that should be characterized each in anatomical-functional terms.

On the basis of the literature available, it can be shown that brain areas which are differentially activated in past and future remembering tasks are indeed specifically involved in the appearance of past awareness and future awareness respectively. Past awareness is in all likelihood mediated by orbitofrontal cortex, a structure also known for its implication in the so-called anticipative cognitive phenomena (Bechara et al. 2000, in press; Burgess et al., 2000, 2001; Okuda et al., 2003; Buckner and Carroll, 2006, Simons et al., 2005). The presumptive neural basis of past awareness is less clearly defined. Confrontation of data from recent empirical and theoretical studies on episodic memory (Ranganath et al., 2004; Wheeler and Buckner, 2004; Simons et al., 2005; Yonelinas et al., 2005; Daselaar et al., 2006; Vilberg and Rugg, 2007) designates the posterior hippocampus, the posterior parahippocampal gyrus, the left inferior lateral and the left inferior medial parietal cortex as being possible neuroanatomical substrates. Although parietal structures are generally thought to play a relatively secondary role in episodic memory (Rugg et al., 2002; Shannon and Buckner, 2004; Wagner et al., 2005), Bruckner and Wheeler, and Gilboa et al. regard them as the putative basis of the subjective experience of recollection (Bruckner and Wheeler, 2001; Gilboa et al., 2004). Nevertheless, neurophysiological studies on déjà-vu and reminiscence (Bancaud et al., 1994; Bartolomei et al., 2004; Barbeau et al., 2005; Vignal et al., 2007) provide further arguments in favor of the involvement of posterior hippocampal formation in the appearance of the feeling of pastness. These results seem to confirm the existence of specific cognitive factors that confer their respective temporal coloration to past and future memory images, and substantiate the notion that awareness of past and future per se does not depend on the retrieval process of memory images. Moreover, studies on mental imagery have evidenced for a long time that brain areas activated when producing mental images, and notably memory images, are largely the same as those involved in the production of perceptual images, suggesting that sensory contents are fundamentally of the same nature whether they take part in the formation of internally-generated images or in the formation of externally-generated images (Johnson et al. 1988; Howard et al., 1998; Wheeler et al., 2000; Kahn et al. 2004; Prince et al., 2005; Rubin, 2006; Daaselar et al., 2007). There are also good reasons to hypothesize that the various kinds of images that compose our conscious life result from the differentiation of "virgin" mental contents which are originally devoid of any particular experiential coloration. In this respect, autonoetic consciousness should not only consist in experiencing past and future memory images, but also perceptual images and other images such as those we experience while thinking, imagining, or dreaming. In other words, autonoetic consciousness should be referred to all these states of awareness that allow us to experience past, present, and future events of conscious life, and the events that occur in the objective world as well as those that occur in our inner mental life. Thus, it seems that one need to consider every experiential form of consciousness as a cognitive activity of an episodic nature, that is to say, based on the capacity of evoking, differentiating, and apprehending at any time mental contents of some duration in actual experience.

Taken together, these results give considerable support and credibility to the theory of the psychical time of presence. Stern's speculative reflections are not only confirmed in many respects in regard to recent advances in cognitive psychology and neurosciences, but the general model of cognition he proposed appears in addition to that to be an excellent interpretative basis for a variety of facts concerning episodic memory and autonoetic consciousness. More particularly, the theory of the time of presence appears surprisingly consistent with current cognitive issues on perception of the past and of the future. More importantly, it gives a real theoretical legitimacy to the crucial notion of an episode and lays the foundations of a global theory of autonoetic consciousness. Of course the cornerstone of Stern's theory remains, in the present state of science, undemonstrated, since neither extensiveness nor intuitiveness of actual conscious experience, nor a fortiori the existence of a cognitive property like the "time of presence", have been formally evidenced up until now. But such issues may be easily investigated on the basis of modern neurocognitive techniques and methods, not only in connection with research on episodic memory, but also, as suggested before, as a part of the investigations relating to the binding problem. Here also the theoretical scheme elaborated by Stern will likely stimulate the development of a number of original programs of research.

Acknowledgement

The author would like to thank Dr. Raoul Sfeir for reviewing the text.