In scientific or academic discussion the term "apparitional experience" is to be preferred to the term "ghost" in respect of the following points:
Attempts to apply modern scientific or investigative standards to the study of apparitional experiences began with the work of Edmund Gurney, Frederick William Henry Myers and Frank Podmore , who were leading figures in the early years of the Society for Psychical Research. Their motive, as with most of the early work of the Society, was to provide evidence for human survival after death. For this reason they had a particular interest in what are known as ‘crisis cases’. These are cases in which a person has a quasi-perceptual experience of someone at a distance at the time of that person’s death or other crisis. If the temporal coincidence of the crisis and the distant apparitional experience cannot be explained by any conventional means, then the presumption is made that some as yet unknown form of communication, such as telepathy (a term coined by Myers) has taken place.
While the extent to which the work of Gurney and his colleagues succeeded in providing evidence for either telepathy or survival of death is still controversial, the large collection of firsthand written accounts which resulted from their painstaking methods still constitutes a body of valuable data concerning the phenomenology of hallucinations in the sane.
A notable later discussion of apparitional experiences was that of G.N.M. Tyrrell, also a leading member of the Society for Psychical Research of his day. Tyrrell accepted the hallucinatory character of the experience, pointing out that it is virtually unknown for firsthand accounts to claim that apparitional figures leave any of the normal physical effects, such as footprints in snow, that one would expect of a real person. However, Tyrrell develops the idea that the apparition may be a way for the unconscious part of the mind to bring to consciousness information that has been paranormally acquired – in crisis cases, for example. He introduces an evocative metaphor of a mental ‘stage-carpenter’, behind the scenes in the unconscious part of the mind, and constructing the quasi-perceptual experience that eventually appears on the stage of consciousness, so that it embodies paranormal information in a symbolic way, a person drowning at a distance appearing soaked in water, for example.
The study and discussion of apparitions took a different turn in the 1970s, with the work of Celia Green and Charles McCreery. They were not primarily interested in the question of whether apparitions could shed any light on the existence or otherwise of telepathy, or in the survival question; instead they were concerned to analyse a large number of cases with a view to providing a taxonomy of the different types of experience, viewed simply as a type of anomalous perceptual experience or hallucination.
One of the points that was highlighted by their work was point (2) listed above, namely that ‘real-life’ accounts of apparitional experiences differ markedly from the traditional or literary ghost story. These are some of the more notable differences, at least as indicated by their own collection of 1800 firsthand accounts:
Apparitional experiences have relevance to psychological theories of perception, and in particular to the distinction between top-down and bottom-up approaches (cf. article on Top-down and bottom-up design). Top-down theories, such as that of Richard Langton Gregory, who conceives of perception as a process whereby the brain makes a series of hypotheses about the external world, stress the importance of central factors such as memory and expectation in determining the phenomenological content of perception; while the bottom-up approach, exemplified by the work of J.J. Gibson, emphasises the role of the external sensory stimulus.
Apparitional experiences would seem to lend support to the importance of central factors, since they represent a form of quasi-perceptual experience in which the role of external stimuli is minimal or possibly non-existent, while the experience nevertheless continues to be phenomenologically indistinguishable from normal perception, at least in some cases.
The interest of apparitional experiences to psychology has acquired an added dimension in recent years with the development of the concept of schizotypy or psychosis-proneness. This is conceived of as a dimension of personality, continuously distributed throughout the normal population, and analogous to the dimensions of extraversion or neuroticism. As long as mental illness is regarded under the disease model, according to which a person either does or does not ‘have’ schizophrenia or manic depression, just as a person either does or does not have syphilis or tuberculosis, then to talk of the occurrence of an apparitional or hallucinatory experience in a normal person is either an oxymoron, or to be taken as an indication of latent or incipient psychosis. If, on the contrary, a dimensional view of the matter is taken, it becomes easier to conceive of how normal people, more or less high on the putative schizotypy dimension, might be more or less prone to anomalous perceptual experiences, without their ever tipping over into psychosis.
Green and McCreery’s identification of a class of what they called ‘reassuring apparitions’ is of particular interest in this regard, as it suggests that the experiencing of hallucinations may even have an adaptive effect in certain subjects, making them better able to cope with adverse life events. This would fit with the model of schizotypy as essentially a normal dimension of personality, and might help to explain why the proneness to anomalous perceptual experiences has apparently not been ‘weeded out’ by the process of natural selection.
Apparitional experiences also have implications for the philosophy of perception. The occurrence of hallucinations, that is, perceptual experiences 'having the character of sense perception, but without relevant or adequate sensory stimulation […]' , have long been one of the standard objections to the philosophical theory of direct realism. According to this theory we are in some sense in direct contact with the external world when we seem to be perceiving it, and not merely in direct contact with some mediating representation in our mind, such as a sense-datum or an image, which may or may not correspond to external reality. The psychologist J.J. Gibson, referred to above, became an advocate of the philosophical theory of direct realism.
Hallucinatory experiences reported by sane people do not pose any new problem in principle for the theory of direct realism, other than that posed already by the more widely discussed hallucinations reported by people in a state of psychosis or under other abnormal conditions such as sensory deprivation. However, they do pose the problem in a particularly stark way, for the following reasons:
In the case of hallucinations reported to have occurred in pathological or abnormal states there is some scope for uncertainty about the accuracy, or even the meaning, of the percipient’s verbal report. Horowitz, for example, summarising his experience of questioning chronic schizophrenic patients about their visual experiences during painting sessions, wrote:
'It was necessary to persist beyond initial verbal descriptions of their hallucinations, and insist that the patient describe and draw what he had seen. Initial descriptions of "vicious snakes" might then be drawn and redescribed as wavy lines. "Two armies struggling over my soul" arose from the subjective experience of seeing moving sets of dots. "Spiders" might be reduced, when the patient stated and drew what he actually saw, to a few radiating lines. In drawings of their hallucinations patients could often distinguish between those forms which duplicated what they saw with their eyes from those forms which were what they "made out of it".'
Such difficulties of interpretation are much less obvious in the case of written reports by ostensibly normal subjects, in good health and not medicated at the time of the experience.
As mentioned above, at least some of the apparitional experiences reported by normal subjects appear to mimic normal perception to such a degree that the subject is deceived into thinking that what they are experiencing actually is normal perception. Similar close mimicking of normal perception is reported by the subjects of some lucid dreams and out-of-body experiences, which therefore pose similar problems for the theory of direct realism.
Apparitional experiences appear prima facie more compatible with the philosophical theory of representationalism. According to this theory, the immediate objects of experience when we are perceiving the world normally are representations of the world, rather than the world itself. These representations have been variously called sense-data or images. In the case of an apparitional experience one might say that the subject is aware of sense-data or images which happen not to correspond to, or represent, the external world in the normal way.
The philosophical implications of hallucinatory experiences in the sane are discussed by McCreery. He argues that they provide empirical support for the theory of representationalism rather than direct realism.