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Tracings of the mind: the role of hallucinations, pseudohallucinations and visual memory in Franco-Cantabrian cave art
First posted: 5 December 2006
Franco-Cantabrian cave art continues to be the focus of much speculation but despite the many theories put forward there has been little progress in explaining the range of perplexing features typical of this "art." Only by regarding such wide ranging and anomalous characteristics as central to this debate might some progress as to derivation be possible. The account presented in this paper will demonstrate how the many "contradictions" of parietal art provide an important indication as to its provenance that can be explained through an understanding of how visual imagery is processed by the brain in the context of the everyday lives of Upper Palaeolithic communities. In this regard, classic hallucinatory experiences, although useful in understanding the various mechanisms of the visual system, are held to be of limited explanatory scope. An alternative, but related, type of visual imagery, known as pseudohallucinations, is therefore proposed as more appropriate in this context. After first defining orthodox hallucinations and how the visual system functions, pseudohallucinations and their causes will then be explained; this will be followed by a discussion of how such mental imagery can be applied to palaeoart in a way that accounts for the wide range of anomalous features prevailing,
Understanding how hallucinations relate to the brain in terms of visual memory and the external visual world can provide important insights into questions concerning cave art. In this respect, some authorities maintain that the perception of everyday visual reality is a type of hallucination (Collerton et al. 2005). In one sense this is correct because it is based on the idea that what we see is an interpretation of the visual world and not the world itself (Dror 2005). In other words, it is a representation of visual reality that depends on the perceiver rather than "objective reality." The difference resides in the fact that the ability to perceive the real world has been moulded by long-standing evolutionary events involving the practical interaction with objects decisive to human survival (Shepard 2001). So, although we see a representation of the external world, this representation has nevertheless been tempered by how the human visual pathways have been shaped by long-standing evolutionary concerns - and it is one, in the normal course of events, in which we all have a common share, thereby allowing access to an agreed, but unstated, conception of visual reality.
Visual information arising from external stimuli accordingly serves to direct as well as inform the visual system that the world is being correctly interpreted. In short, normal visual awareness is kept in line by visual information deriving from the world at large that directs the higher order correlates of visual imagery and memory (Collerton et al. 2005). This is not a one way process, however, as there is much cross-referencing and feedback involved, including from the highest back to the earliest levels, especially when more detailed scrutiny of a stimuli or visual imagery is required (Kosslyn and Thompson 2003). It is when the balance, for whatever reason, between incoming visual signals and the various pathways by which these are represented, is disturbed that hallucinatory-like episodes tend to arise (Collerton et al. 2005).
The abnormal visual brain and hallucinations
Early researchers found that stimulation of certain areas of the visual cortex can lead to the activation of visual memories and hallucinatory type objects (Penfield and Perot 1963, Horowitz et al. 1968). The particular areas involved were subsequently identified with more specificity, particularly the inferotemporal cortex. This part of the brain, especially the inferotemporal area, is acknowledged as the place where visual imagery is stored for the purpose of recognition and visual memory- that is, it is where visual templates are to be found that allow the matching of incoming visual information with previously assigned templates (Logothetis and Sheinberg 1996; Logothetis et al. 1995). A finding which has been verified by the fact that this area is highly active during episodes of both REM dreaming (Schwartz and Marquet 2002) and hallucinations (Collerton et al. 2005). Humans are therefore a species with a particular bias for perceiving objects which explains why the temporal cortex seems to have undergone enlargement in hominins (Rilling and Seligman 2003) and visual memory has become so important. Disturbance or damage to any part of this pathway can lead to the accentuation of processing in preserved areas. There are a number of ways by which a disturbance can be generated - usually through over or under stimulation of the pathways by way of psychoactive drugs and prolonged isolation respectively, or through brain pathology (Joseph 1990). There is a further, and for our present purpose, very important means by which "hallucinations" can be induced, one that is ignored by most investigators. This concerns how the visual pathways respond to everyday experiences involving various states of stress, anxiety, or over activity in the face of crucial life-events. For the moment, however, I wish to concentrate on the hallucinations experienced when intoxicants are introduced into the nervous system as this will provide a clearer picture of how visual images arise in the visual cortex.
Over stimulation of the visual brain through the use of psychoactive drugs such as psilocybin, mescaline or LSD etc., leads to a situation where internally derived signals intrude on visual information coming from the external world. This is realised through the opening of extra serotonin channels at synapses so more information flows spontaneously through the system (Kalat 1998). As a consequence, visual templates at higher levels (with which humans are particularly well equipped), including visual subcortical structures, will tend to disgorge their contents with little or no inducement due to the fact that the thresholds that trigger these have been lowered (Joseph 1990). Although incoming visual data may still be influential, its effects are reduced and more often serve as a basis for projections based upon previously stored visual templates and over-active limbic structures - a scenario that also occurs in the normal course of events but now, thanks to lowered thresholds, inappropriate templates are often elicited that have little or nothing to do with the originating stimulus. This process is likely to begin with a distortion of external stimuli that can become so extreme alternative, but erroneous, interpretations are likely to occur.
The normal visual system, visual memory and imagination
It has been established that there is a common neurophysiological mechanism underlying visual representation, whether this is perception, imagining, thinking, dreaming or memory (Shepard 1984, Kosslyn 1994, Farah 2000). Crucially, Kirby and Kosslyn (1992:72) propose that visual memory, as such, evolved out of the perceptual and recognition system. What differentiates the various levels of the system depends on whether it is being stimulated by incoming visual data from the real world, whereupon the accent will be on the early to middle stages, or is being directed from the need to reflect on events whereby the later stages will come to the fore. This is consistent with the experienced visual world being a product of interactions between abstract top-down visual memory templates and bottom-up sensory ones, with the former generally more influential in subjective perception. Subjective perception can therefore be the consequence of dynamic reciprocal interactions among external sensory input, internal object and scene representations and goal directed attention. This is promoted by top-down biasing of information as a consequence of familiarity with objects, individual goals, and expectancy that will influence the speed and accuracy of object awareness (Collerton et al. 2005).
Visual memory therefore appears to be underwritten by a system that is shared, but weighted asymmetrically according to priorities, and one of its properties is the propensity to suggest alternatives when confronted with ambiguity, as when one attempts to disambiguate a camouflaged or indistinct form (Mast 2005). Such an ability would have been crucial to hominins as an automatic system that is able to quickly furnish a host of different "suggestions" to the identity of any ambiguous form that would have led to greater survival rates for those so disposed. The propensity of the higher end of the visual hierarchy to automatically "suggest" alternatives in this way is a mechanism useful when danger threatens as well as a device for preparing for actual situations. In this respect, Kosslyn and Shin (1994) emphasise thatimagery selectively facilitates perception, so that if subjects imagine a form they will be more likely to detect a degraded version of a shape when presented with alternatives.
Visual imagination seems to be an aspect of the visual system closely related to visual memory and one that is most "detachable" from everyday reality in that it allows possible scenarios to be played out completely disengaged from the real situation. The obvious benefit of this capacity resides in the opportunity to rehearse situations so that in the real situation one is more able to deal with the unexpected. An important outcome of this would have been an ability to project content and meaning onto objects that may or may not have any resemblance to things in the real world. This is an ability with which humans, even at a young age, (Cox 1995) are particular well equipped to the extent that they are able to project meaning and value on to quite neutral objects.
The influence of psychoactive agents
The visual system, because it is highly tuned and multifaceted, is prone to volatility as a consequence of either injury or the ingestion of intoxicants. The taking of psychoactive drugs especially serves to introduce a measure of instability because they provide an internally-derived agent that plays havoc with how these systems interrelate. As a result, the processes of imagination and projective interpretation can come to the forefront of awareness as variously spontaneously generated stimuli emerge, distort, deform, coalesce, dissipate and re-emerge in multiple ways. The system is actually trying to make sense of the mixed and contradictory signals issuing from both external sources and within the system itself. Thanks to the interpretative ability of visual imagery, a struggle to make sense of the internally produced stimuli ensues whereby different "hypotheses" are generated as to the likely identity of the manifest ambiguity. And because of the shifting effects of the drug on various parts of the system, there is a tendency for a changing set of "hypotheses" in the form of possible interpretations to be presented (Mast 2005).
These effects are not just a result of the opening of extra channels in the nervous system but also a consequence of the instability that comes when the normal markers that constrain the system are lacking to the extent that there is little onto which the system can latch other than self-generated stimuli. This volatility applies just as much to the processes of imagination due to its natural tendency to disengage from visual reality. In fact, it may be the imaginative faculty's propensity to range more freely under the effects of psychoactive drugs that leads to the hallucination of monsters, angels, hybrids, fabulous things and strange creatures (Shanon 2002).
We have described how hallucinations arise when the brain is in an abnormal state, which can be informative as to how the visual system operates when performing its usual tasks. The normal visual system, however, is not immune to error as is evidenced by what is termed "The Perky Effect" (Perky 1910). This shows how the division between imagination and visual reality can be quite fluid. Perky placed observers in a dimly lit room and asked them to stare at a blank screen some distance away. The observers were then asked to summon up an image of a particular object and while preoccupied with this (and still staring at the screen), Perky surreptitiously projected a barely visible image of the same object onto the screen. To simulate the effect of a mental image, the projected object was agitated slightly to create a shimmering effect. Nearly all the observers remained oblivious to the attenuated screen projection and thought that what they were seeing was their own internally derived mental image. Even after the participants had been informed that what they had witnessed was a real projection, most observers insisted that they had imagined what was there. This effect has been subsequently confirmed by other investigators (Segal and Fusella 1970, Reeves 1982). These experiments add weight to the notion that our hold on "visual reality" is tenuous and we are liable to be fooled or make errors in certain situations. In other words, imagery can intrude on reality and reality on imagination. Other studies on the nature of visual imagery have found that there is a loss of high spatial frequencies thereby reducing the amount of detail thus causing a certain blurring of the remaining outline contours. (Harvey 1986, Sekuler and Blake 1994 see especially figures 13 and18: 485)
The "normal" visual brain and pseudohallucinations
In contrast to hallucinations, pseudohallucinations are defined as imagery that is not usually mistaken for perception (Davis 1987). Moreover, classic hallucinations appear to exist in objective space whereas pseudohallucinations reside in subjective space (Whitlock 1987). Following Sims 2003, Jaspers (1963) and Aggernaes (1972) the main differences between hallucinations and pseudohallucinations can be summarised in figure 1.
Figure 1. The different kinds of experiences associated with hallucinations and pseudohallucinations.
It is obvious from figure 1 that there are important distinctions dividing the two categories. However, there may be an element of gradation linking or bridging the two. In this sense, Kraüpl Taylor (1979) refers to pseudohallucinations as a special type of hallucination. Moreover, pseudohallucinations may occupy a position in a continuum located between full-blown hallucinations, visual imagery and the everyday perception of the real world (Jaspers 1963). In this regard, there is also a gradation linking the former to the latter. It is important to emphasise, however, that even though pseudohallucinations are not perceived as real they can still have an emotionally charged dimension (Horowitz 1975). And, as we shall see, although one of the differences between hallucinations and pseudohallucinations resides in the fact that, in the latter case, the individual has insight into the fact that the image is not real, in some circumstances this boundary may also become permeable.
Interactions between these various influences are outlined by Horowitz (1975) in stating that internal representations come to the fore due to several reasons: 1. Relative reduction of external input with no concomitant lowering activity in the representational system. 2. Increase in activity of the representational system without increase in availability of external signals. 3. Augmentation of internal input due to arousal of ideas or feelings secondary to drive states. 4. Reduction of usual levels of inhibition over internal inputs. 5. Alteration of the dynamic between different contingencies permitting internal inputs to gain more representation over direct perception. Jaspers (1963) is also careful to make the point that these categories can combine in various ways according to the mental state of the individual. The relationship between these various categories is summarised in figure 2.
Hallucinations -------- Pseudohallucinations --------- Visual Image -------- Sense Perception
Figure 2. The various dynamic relationships along a continuum linking sense perception, visual imagery, pseudohallucinations and hallucinations with regard to external stimuli and subjective experience.
The effects of the realignment of these various factors can be seen in distinct psychological states, examples of which will now be described. Although in normal circumstances a memory image fades quickly, becoming less detailed, images associated with conspicuous events tend to be retained longer (Vernon 1971). This can be in response to traumatic events, such as a disaster, involving shock. One example is the shell-shock experienced by soldiers during the First World War who often re-enacted the original disturbing event in the form of recurring flashbacks (DSM 1994). Flashbacks are part of the cyclical reliving of the original episode which may be a coping mechanism whereby the mind attempts to familiarise itself with a situation as a safeguard against a repetition of the same event so that an appropriate level of mental defence is readily available. In such cases, the emotional memory is centred on the limbic system which has been so adversely affected that the system endeavours to make amends through a replaying of the distressing circumstances (Horowitz 1975). Brewin (1998) defines such disorders as "The curse of perceptual reminiscence is a cardinal feature of post-traumatic stress disorder (PTSD) in which sufferers attempt to avoid but cannot prevent vivid, emotionally arousing images repeatedly intruding into their waking lives...". These visual memories can be experienced several times a week lasting anywhere from a few minutes to one hour (Gross 2005). As well as in response to extreme shock, Horowitz (1975) also found intrusive and stimulus repetitive images of this kind experienced in over 50% of cases where individuals had suffered mild to moderate emotional shock, thereby emphasising the widespread nature of the phenomenon. Similarly, with the mental disturbance that comes with the bereavement of close kin, whereby a complete stranger is often mistaken for the deceased person (Grimby 1998; Lange et al.1996; Kraüpl Taylor 1979). The stimulus driving these quasi-hallucinatory episodes is not a psychoactive agent or damage to the brain but rather the hyper-aroused limbic regions that provoke the necessary imagery in higher visual centres (Joseph 1990). In such cases, the imagery may also be manifest in dreams or nightmares. Anything that might provoke over-arousal in these systems may therefore elicit a pseudohallucination (Manford and Anderman 1998). The likelihood of a Perky-like effect occurring (mistaking an internally generated image for one based on external reality) is therefore greatly increased in such cases of heightened arousal.
Another example of a mental state leading to a quasi-hallucinatory episode is when an individual undergoes intense fatigue - the opposite of arousal but still a disturbed conscious state. Those so affected often report seeing objects of various descriptions, invariably animals. For example, drivers who endure long and monotonous journeys on motorways through fog, snow-storms or at night often report seeing non-existent animals which they swerve to avoid before the mistake is realised (McFarland and Moore 1957, Whitlock, F. A. 1987). In these cases, the attention to external stimuli is attenuated allowing visual imagery to come to the fore. Pseudohallucinations are also likely to be experienced in cases of isolation or intense emotional need e.g. shipwrecked sailors often visualise a boat coming to the rescue. Pseudohallucinations may also arise due to purely physical causes such as when an individual endures hunger or thirst (Gross 1992, Sandford 1936) wherein the mental image of the item in question becomes increasingly intrusive until the need is placated.
Correspondingly, where prolonged concentration on particular objects is required individuals often report intrusive mental images of the items subsequently appearing. For example, medical students and laboratory technicians, on learning to count blood cells for long hours through a microscope, later report seeing intrusive hypnagogic images of cells (Horowitz 1975). Motorists also report the occurrence of visual images of headlights after night-time driving. These experiences, it seems, can be quite startling because they enter awareness involuntarily and cannot easily be erased. It is as if the image of the object involved has become so imprinted in neural circuits that it springs to mind even in the absence of the real stimulus. This effect may also be reinforced by the fact that when engrossed in intensely focussed activities attention is withdrawn from external reality.
All of the above examples illustrate how pseudohallucinations are likely to be experienced by the ordinary population as part of "normal" experience and need not be confined to exceptional or abnormal groups. Furthermore the division between what is real and what constitutes a mental image can fluctuate according to the potency of environmental conditions and the intensity of psychological contingencies. As Helvenston and Bahn (2005) have stipulated the causes of altered states of consciousness can be many and varied. The experiences leading to pseudohallucinations described here may be an important variant class of such altered states that have crucial implications for understanding cave art.
Pseudohallucinations and Franco-Cantabrian cave art
The diverse ways be which quasi-hallucinatory phenomenon are induced can be informative as to why there are so many images of animals in Franco-Cantabrian palaeoart and the reasons for their depiction. Most of the conditions cited above come together in the caves visited by Upper Palaeolithic people. It is highly unlikely that these communities would have resorted to psychoactive drugs or similar (Helvenston and Bahn 2005) and therefore classic hallucinations as an explanation in this context can be discounted (see Hodgson 2006 for further reasons).
So how might "hallucinations" be relevant to understanding the depictions of animals in Franco-Cantabrian caves? The answer lies in approaching the question in the context of pseudohallucinations as defined. We have shown how hallucinatory episodes of this type can be induced by certain types of experience relating to "normal" interaction with the world. It is by examining Upper Palaeolithic communities in these terms that we might be in a better position to assess how quasi-hallucinations can be relevant to cave art. Fatigue, various kinds of trauma, over-concentration on particular items, intense emotional or physical needs and stress related events have been identified as prime examples of causes that can evoke pseudohallucinations. Moreover, individuals often find these kinds of hallucination so compelling that they are sometimes treated as real (Sims 2003), which provides an important pointer as to what might have motivated the Franco-Cantabrians to create parietal art.
It is uncontroversial that adverse experiences would have been a regular occurrence in the daily lives of Cro-Magnons. The animals of the Upper Palaeolithic were more common, varied and larger than today's and included carnivores of various descriptions as well as huge herbivores (Hodgson and Helvenston 2006). On hunting forays focussed concentration would have been necessary for sustained periods to acquire the essential protein rich meat as well as to maintain vigilance in case of marauding predators (this, however, does not presuppose the much criticised idea of "man the hunter" but merely that all member of the community would have been involved in hunting activities to a greater or lesser extent). As noted, one of the effects of raised and prolonged concentration levels, especially during high states of arousal, is that the sought-after items come to be imprinted in neural circuits. In this respect, it has been established that noradrenergic activation in the amygdala enhances and reinforces memory (McGaugh 2006). Mental fatigue is a hallmark of this level of focussed attention that would have been exacerbated by the extreme physical exertion involved in tracking game. Post-traumatic stress will also have been a contributory factor because it is probable that members of the hunting party would have met their death, either by way of carnivores targeting humans or the sought-after prey, such as bison, rhinos and aurochs trampling on victims (the "fallen man" of Lascaux may be a representation of one such event). Hunger, if not starvation, will have been another ingredient added to this mix (Hodgson 2006) for, as emphasised, lack of sustenance leads to an image of the food in question spontaneously coming to mind. In this respect, mental states play a vital role in how perceptual information is processed to the extent that the hopes, fears and expectations affect what is perceived (Dror 2005). On returning to a cave in search of protection, the dim conditions meant that the constraining effect of external stimuli would have been reduced whilst, thanks to recent stress-related experiences, visual imagery would have come to the fore (bright light improves perception of external objects and, in this sense, discourages pseudohallucinations [Collerton et al. 2005]).
In such an environment, various members of the group would, in all likelihood, have experienced pseudohallucinatory images of animals, sometimes compounded by flashbacks. Given the daily stresses of Upper Palaeolithic life, it would have been almost certain that hunter-gatherer groups did experience such mental aberrations. This would have been reinforced, and has obvious parallels with the Perky Effect, in that many of the contours of the dimly-lit cave walls simulate animal outlines. That is, there would have been an ambiguity between the subjectively induced image and the suggestive, undulating contours of the walls - an ambiguity that would have been reinforced by the fluctuating light, and shadows cast, of lamp burners and fires. This ambiguity would have been an important motivational factor inducing the visitors to render the mental image permanent. The fissures of cave walls that were assimilated into some depictions corroborates this hypothesis because their suggestiveness will have served to stimulate visual imagery just as much as the contours of the cave seemed to. It has been estimated that at least 10-15% of cave art involves the incorporation of natural features that are suggestive of an animal's anatomy (White 2003).. This is probably an underestimation as many of the original rock features on which the animals were based will have disappeared (e.g. natural stains and blotches as well as shadows projected on to walls by intervening surfaces, concretions and rock formations). Suggestive features of this order can be regarded as highly potent triggers that will have helped encourage and reinforce a visual system already hyper-sensitised to animal forms. The exploitation of natural features that simulate animals provides a vital clue as to the relevance of pseudohallucinations and visual memory as regards this art. This is reflected in the fact that, on hunting expeditions, when confronted by a threatening animal the raised arousal levels generated served to keep the individual in a state of vigilance so that the slightest cue suggestive of a predator would have elicited an image of the same or similar. This is because it is safer in this situation to assume a predator is still close by and respond to the slightest cue that might indicate a threat than to wait until a more explicit cue is forthcoming - an effect known as adaptive conservatism. On returning to a cave or rock shelter, vigilance levels would still have been in a high state of readiness with the effect that any slight resemblance to an animal outline in the shifting light and shadows cast onto the undulating walls would have been enough to evoke a visual image of fauna.
Horowitz (1975), in relation to pseudohallucinations, points out that an ambiguous shape (such as a fissure or undulating surface of a cave) can be "illusioned" into either an item of food, if the subject is hungry, or sexual anatomy if in a state of heightened sexual arousal (which has implications for the vulva iconography in cave art), and so on. And once an hallucinatory-like image has been experienced in a particular setting it is inclined, in future, to come to mind more easily in that venue through association (Collerton et al. 2005) which further explains why caves became a favoured location for the making of palaeoart. The fact that graphic images are found in the deep, more inaccessible, parts of caves is explained by the fact that pseudohallucinations would have been as likely to occur in these areas as in the more accessible chambers.
One of the characteristics of pseudohallucinations (and imagery) is that they tend to be in the form of a single representative example of a class or category (Collerton et al. 2005, Vernon, 1971). For animals, this is the typical viewing profile (see Hodgson 2003b for a discussion), a common trait in Upper Palaeolithic depictions as Halverson (1991) has demonstrated wherein the contour outline defines the class. Another characteristic of pseudohallucinations is the fact that only the main defining aspects (diagnostic features) of the object are included in the subjective image in that the features more attended to during interaction with an object tend also to be those liable to accentuation (Henderson et al. 2001), which, again, matches exactly the characteristics of Franco-Cantabrian art. For example, the lower extremities of an animal's legs are regularly omitted whereas the upper diagnostic features are invariably included (Fritz 1999, Hodgson 2003b). Interestingly, Jaspers (1963) reports the case of a patient hallucinating benign-looking "prehistoric animals" where, occasionally, one item of anatomy would become prominent yet the rest of the form appeared harmonious to the extent that the animals represented a particular type usually bereft of movement. Although the individual concerned was schizophrenic, the example illustrates how hallucinations of animals seem to coincide with many of the features of fauna depicted in cave art.
The outline contour of pseudohallucinatory images has been shown to be incomplete or liable to various levels of fading or accentuation according to the psychological state and level of awareness of the person concerned. One of the predominant aspects of parietal art is not just the concern for the contour but also the abbreviation of this outline in various ways (the more complete figures of Lascaux are an exception). In fact, the indistinct outline seems to be one of the commonest traits of parietal art that was intended and not a result of natural deterioration (Ucko and Rosenfeld 1967). As well as a tendency to fade, one other notable characteristics of a quasi-hallucination is the loss of high spatial frequencies causing a certain fuzziness around edges and borders (and reflects the shimmering of the Perky effect). Upper Palaeolithic Cave art abounds in such outlines (Ucko and Rosenfeld 1967: 58), the representations of Chauvet being prime examples with many at Lascaux displaying similar traits as well as the horse panel at Ekain (Guipúzcoa). This is achieved either through multiple lines (often mistaken for attempts at producing perspective), the rubbing and smearing of contours, or the blowing of finely sprayed pigment onto surfaces. Although some animal outlines were drawn after preparation of the walls, the actual finished drawing was nevertheless often smudged hence creating a blurred quality (see Clottes 2003). Having said this, there are some depictions that show a concern for the more detailed aspects of an animal's anatomy. In fact, the more precise outlines can also be explained by quasi-hallucinatory effects in that the latter can often display more definite edges (Jaspers 1963) depending on the intensity of the experience. Otherwise, such portrayals may simply represent those depictions that were chosen from a previous corpus of outlines for further embellishment for any number of possible reasons (see below).
Another curious aspect of this art is the disregard for the scale of animals portrayed in the same "scene," which parallels the fact that the visual image of pseudohallucinations is subject to size distortions to the extent that an image can range in size from the small to relatively large (Jaspers 1963). The repetitive nature of cave art images also coincides with the repetitive images of pseudohallucinations. A further unusual characteristic is the juxtaposition of animals not normally seen together, which is all the more surprising given that some authorities claim that the hunters responsible for cave art were astutely aware of the behaviour of the various fauna (Clottes 2003). Because pseudohallucinations are unpredictable, intrusive and tend to linger, a species of animal is likely to have been seen against any number of previously executed portrayals thereby leading to the incongruous assortment of animals. This analysis explains why there are so many repeated outline contours of animals in palaeoart, often with no regard to the position of a previously drawn figure. Having created a preliminary outline, the enduring visual image will have served as the stimulus/template for a second graphic representation somewhat offset from the first.
It is possible that when hunters sought shelter and rest in a cave they will have laid on the ground and looked u at the dimly-lit ceiling and viewed pseudohallucinations projected there. They will certainly have taken advantage of these havens for short bouts of sleep with all this entails for dreaming and the various levels of awareness existing between wakefulness and unconsciousness that would have included various states of drowsiness (the interlopers did not seem to use the caves for living or as sleeping places but nevertheless are thought to have used the cave entrances for this purpose). Dream images often persist into consciousness and can sometimes be quite vivid and alarming especially when an individual suddenly awakes. The subject matter of dreams is thought to be driven by emotionally charged memories with other themes determined by current concerns and daily activities - in this respect the fear response is triggered by the amygdala and is more active during REM sleep (Schwartz and Marquet 2002). The various levels of arousal and alertness associated with drowsiness suggest that, thanks to the everyday interaction with animals on many levels, the subject matter of the dream images of cave visitors would often have been about such interactions that were manifested in pseudohallucinations during periods of drowsiness. To reiterate, although the Palaeolithic people did not sleep in the depths of the caves they nevertheless will have experienced various states of drowsiness after coming round from sleep in or near the cave entrance.
The many densely packed superimpositions to be found on cave ceilings seem puzzling to the modern eye but to the Palaeolithic hunter they were a kind of record of the persistent quasi-hallucinations seen against the backdrop of ceilings and already painted surfaces. The haphazard orientation of these superimposed depictions is explained by the fact that, from a prostrate position, and for any of the aforementioned reasons including hypnogogic states, hunters gazing upwards at this ceiling would have viewed pseudohallucinations from a number of different positions (even from a standing position the ceiling would have been seen from a unique angle). Another curious aspect of cave art is the rotation of figures on walls, such as the "vertical rhinoceros" of Chauvet (Clottes 2003). Rotations of this kind are more frequent on ceilings for reasons already posited and less common on walls due to the fact that the observer's viewpoint is more likely to be dictated by a common standing posture and therefore a shared line of view.
In sum, the reduced light of the cave with its animal-like undulating contours and the highly charged visual system of the human visitors will have come together making certain that pseudohallucinations of animals would have been experienced, thus motivating and directing how animals were depicted on cave walls and ceilings. And it is highly likely that, because Cro-Magnons remained oblivious as to the causes of pseudohallucinations, they would have regarded them as special leading to their attempted preservation in a tangible form. Images of this kind are often referred to as "visions" (Reed 1972) and are sometimes associated with haunting (Lange et al. 1996) which has implications for how Palaeolithic communities might have labelled such manifestations. The main similarities between pseudohallucinations and Franco-Cantabrian cave art can be summarised as follows:
The range of specific factors that would have invoked pseudohallucinations of animals during the Upper Palaeolithic can be further summarised as follows:
Pseudohallucinations allow many aspects of Upper Palaeolithic cave art to be understood more clearly that have previously resisted interpretation. For example, they explain why the depictions are so naturalistic at an early date in the sense that the mental template of the mind's eye would have been immediately available for the purpose of portraying fauna. The fact that these representations endured for 20,000 years in virtually the same format is further corroboration of this explanation in that the same visual image, i.e. the typical viewing profile, will have remained constant. These criteria account for the fact that, although there was, at the beginning, an emphasis on dangerous fauna, a range of animals from carnivores to ruminants are depicted throughout. This is verified by the fact that, during this extended timeframe, the animals portrayed declined from the dangerous to the more benign following a drop in numbers of the former (Clottes 1996). The depicted fauna invariably did not match the diet of Upper Palaeolithic people because the intrusive images at any one time were involuntary and unpredictable and would have been elicited by any number of the above cited factors.
As imagination is, by definition, concerned with putting anomalous things together in multifaceted ways, strange beings and beasts such as chimera and therianthropes are likely to be elicited. Therianthropes can thereby be explained as follows; on viewing a previously portrayed animal an individual may, at the same time, have been experiencing an pseudohallucination of a particular species of which the body parts (which could have been an item of human anatomy) would have been seen against a previously made graphic image thereby leading to the perception of an apparent hybrid figure. This accounts for the scarcity of therianthropes, as those responsible for the portrayals will have been, for reason already alluded to, fixated more on the outlines of animals. This factor needs to be added to the list of explanations that may have inspired amalgamated figures and does not discount the probability that such hybrids could also have been hunters in disguise (Guthrie 1984) or perhaps expressing the generativity that comes with an imaginative faculty given free reign in the dim surroundings of the cave that may have also been inspired by mythic concerns (Hodgson and Helvenston 2006).
These contingencies will have been further underwritten by the aforementioned fact that animals were integral to the evolution of the human brain to the extent that the encoding of animal forms seems to have become a dedicated, hard-wired module of the temporal cortex (Caramazza and Mahon, 2006, Hodgson 2003b, Hodgson 2006). This is supported by the fact that studies of eye movements when viewing complex scenes have found that attention gravitates more to people and animals than inanimate objects (Yarbus 1967). Implicit perceptual processes are also relevant in this regard, as it has been established that recent and repeated visual exposure to the same object has a tacit (subconscious) influence on visual memory recall (Hodgson 2003a). Taken together with the fact that animals continued to be a crucial aspect of the everyday lives of Cro-Magnons, it is incontrovertible that the profiles of fauna often came to the mind's eye of such individuals thus explaining why animals were so pervasive in this "art." Moreover, the fact that the majority of animal profiles are abbreviated to a greater or lesser extent led to the advantage that, when it came to identifying animals in the wild, this would have led to significant gains in perceptual sensitivity to such forms. The depictions in caves may well have also been deliberately accentuated or obfuscated according to these parameters as a means of exploiting the depicted image (Hodgson 2003a). Indeed, as Kirby and Kosslyn's (1992) observe, imagery plays a special role in identifying objects in "noisy" visual environments and in this sense the depleted and superimposed outlines of animals will have served to stimulate mental imagery and may also have acted, by way of positive feedback, to inspire the making of yet further outlines.
This account specifically relates to Franco-Cantabrian cave art showing how two-dimensional cave art may have arisen. It is probable that the depictions created in this way came to signify and acquire value beyond that of pseudohallucinations, which is suggested by the numerous and varied portable objects on which fauna are also depicted. Moreover, it is highly likely that pseudohallucinations and their graphic counterparts would have been regarded as special. The fact that modern-day humans sometimes refer to such images as "visions" is informative in this respect. What such imagined and depicted images meant to Palaeolithic people is however beyond the scope of this analysis but is, nevertheless, provocative. This theory is therefore not a "one size fits all account" as has been the case with so many other theories that have tried to explain the paradoxes of parietal art but an attempt to explain some of its. more enduring aspects. How these images and their graphic equivalents were interpreted is yet to be ascertained and remains the province of archaeologists and anthropologists.
One of the advantages of this theory is that it is open to falsification. For example, an experiment could be devised whereby subjects might be given an identification task involving prolonged concentration on pictures of animals thereby simulating the perceptual activity with which Upper Palaeolithic hunters would have been concerned in locating and searching for animals. The targeted group could then be asked to enter a cave (with suggestive contours) and asked to record what they saw. A control group would simply follow their normal routine and their comments on what they witnessed in the cave also registered . The prediction is that the target group would tend to see more animal forms than the control group. This procedure could be made more authentic by giving the focal group adrenaline to induce arousal that would predict an even greater number of animals would be seen.
The Geometric Patterns and Hand-Prints
One peculiar aspect of this art not addressed so far is the many geometric forms that adorn surfaces often placed alongside animal depictions. Kosslyn and Thompson (2003) make the important point that graphic representations are themselves no more than geometric patterns that depict the appearance of objects. Visual imagery is accordingly regarded as a kind of "sketch" (encodes only the more obvious contour primitives of an object such as the outline) but when greater detail is called for, the lower end of the visual cortex tends to be recruited. As the early visual cortex e.g. V1 and V2, is particularly concerned with the processing of geometric forms, the depiction of such "primitives" (in Gibson's  terms "invariants") adds what Horowitz (1975) terms a "perceptual type of intensity to the resultant constructions." Hodgson (2000a, 2000b) has shown how, because the early visual cortex is especially concerned with processing geometrics, these motifs appear in palaeoart due to the resonance they provoke in lower visual centres. Geometrics therefore both simulate and stimulate the way the visual brain constructs images and were realised in cave art due to the sense of empathy thereby evoked by way of a feedback mechanism. As geometric patterns were, in this way, inherently appealing to their authors, they would probably also have taken on a significance beyond what originally inspired their production.
Hodgson (2006) has made the point that hand prints (both positive and negative) tend to pre-date iconic images e.g. Cosquer (Clottes 2000). They may therefore have been simply a means of creating a relatively acceptable graphic representation by way of a rudimentary technique. This suggests that they could have emerged independently of the animal representations, though it is probable that they did eventually come to be associated with the more complex faunal images in ways that remain obscure. In the present context the hypothesis would be that, when specifically associated with animal outlines, such a feature was a means of testing or gauging the tangibility of animal representations in the face of the intangibility of pseudohallucinations.
The range of phenomena of cave art that can be explained by this account can be summarised as follows:
In addition, the following have the potential to be similarly explained:
Franco-Cantabrian caves served as a particularly favourable location that promoted and encouraged the experience of pseudohallucinations. Hunters seeking refuge in these caves will have been engaged in stressful and demanding situations on expeditions involving highly focussed and prolonged concentration that led to an accentuation of visual imagery at the expense of externally perceived stimuli. This may have been further reinforced by hunger or traumatic experiences in relation to the dangers of tracking game and avoidance of predators whereby survival of the individual hunter regularly came under threat. The classic range of adverse experiences that provoke pseudohallucinations appear to have been common to those inhabiting the Upper Palaeolithic refugium, namely starvation, fatigue, prolonged focussed attention, traumatic events, stress and loss. Because Upper Palaeolithic people would have been unaware of the reasons for the existence of such quasi-hallucinations, it is probable that this imagery came to be regarded as special. Indeed, the dimly lit cave environment may have been particularly associated with "visions" of animals. The fact that the depictions of fauna show many similarities with pseudohallucinations, especially in their incompletness, outline contour, blurred quality, exaggeration of features and single units, strongly suggests that this type of imagery is responsible for Franco-Cantabrian art. Unlike many previous explanations, this account is solidly based on the regular activities of Upper Palaeolithic people as they attempted to survive during the fluctuating climate of the Ice Age - conditions that directly influenced their psychological state which, in turn, determined how parietal art was made.
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