In dualism and reductionism it is easy to see what experiences of the external world represent Percepts of objects ‘in the mind or brain’ represent

the objects we see out in the world. But if experiences of objects and objects as perceived are phenomenologically identical, then what do experiences of objects represent? One may ask the same question about the experienced body and about ‘inner’ experiences.

In the present chapter, I address each of these questions in turn.

Question 1: How perceived physical worlds relate to

the world described by physics

The ‘exper iential mater ials’ from which the everyday physical world is constructed are drawn from a very limited number of sources—five, to be precise. The world we perceive consists of what we see, what we hear, what we touch, what we taste and what we smell. Each modality of experience is consequent on the activation of specific neuronal pathways in the peripheral and central nervous systems. Activation of the optic nerve and visual system is experienced as ‘light’ whether they are stimulated by implanted microelectrodes, by excessive rubbing of the eyes or by impacting photons triggering molecular changes in the photo-pigments of retinal cells. Likewise, activation of the auditory nerve and its projection areas is experienced as ‘sound’ whether produced by direct electrical stimulation, or normally, by air disturbances causing the bending of hair receptors in the inner ear. Sensory systems are committed to specific modalities of experience. It is not possible to produce experiences of ‘light’ by stimulating the auditory nerve or experiences of ‘sound’ by stimulating the optic nerve. Nor can ‘touch’ fibres produce some other sensation such as ‘taste’ or ‘smell’.1

From another point of view, afferent neurons are the living strands that connect our brains to the surrounding world. The sense organs at their tips convert a small selection of the energies sur rounding our bodies into electrochemical changes that activate the neurons to which they attach. Photosensors in the eye respond to electromagnetic energies radiated, reflected and refracted by entities in the external world. Mechanoreceptors in the inner

ear respond to minute disturbances produced by such entities in the surrounding air. Sensors in the skin monitor conditions at the interface of our bodies and the environment, responding to mechanical deformations and thermal changes on the skin surface. Receptors in the nasal cavity and those embedded in the tongue monitor aspects of the chemistry of substances we inhale and ingest. In so doing, these sense organs decide which events are to be experienced as light, which as sound, which as touch and so on—and the systems to which they attach decide the manner in which detected energies are translated into different forms of experience. For our purposes we do not need to review the extensive literature on how this is done.2 _{A few, basic examples will suffice to illustrate} how the world described by physics is translated, by our biology, into a world as experienced.

Translating electromagnetic energy into experienced light

Photoreceptive cells in the eye have extraordinar y sensitivity. As the neuropsychologist Richard Gregory notes,

We cannot with the unaided eye see individual quanta of light, but the receptors in the retina are so sensitive that they can be stimulated by a single quantum, though several (five to eight) are required to give the experience of a flash of light. The individual receptors of the retina are as sensitive as it is possible for any light detector to be, since a quantum is the smallest amount of radiant energy which can exist. It is rather sad that the transparent media of the eye do not quite match this development of absolute perfection. Only about ten per cent of the light reaching the eye gets to the receptors, the rest being lost by absorption and scattering within the eye before the retina is reached. In spite of this loss, it would be possible under ideal conditions to see a single candle placed seventeen miles away.

(Gregory, 1966, p. 19) The range of stimulus intensities that the eye can handle is also impressively wide. The largest stimulus is estimated to be around 10,000,000,000 times the size of the smallest detectable stimulus. On the other hand, the range of electromagnetic frequencies that our eyes are able to detect is very limited. Visible light occupies only a very small bandwidth of the electromagnetic spectrum from around 730 nm (seen as red) to around 370 nm (seen as violet). Beyond the sensitivity of our eyes are radio waves, radar waves, microwaves, infrared and ultra-violet radiation, X-rays and gamma rays. As Gregory puts it, ‘Looked at in this way, we are almost blind’ (ibid., p. 18).

Energies that are detected are translated into events as experienced in ways that bear only a remote resemblance to the simple descriptions of those energies given by physics. For example, as a first approximation, the relation

between the intensity of a white light and its perceived br ightness is described by a simple power function (Stevens, 1966). However, brightness also depends on frequency. Colours in the middle of the visible spectrum appear brighter than those at the ends. A 100-watt light bulb painted yellow, for example, appears brighter than one painted blue or red. The relative brightness of different colours also varies from night to day. In daylight, when the eye is light-adapted, reds appear brighter than blues. When the eye is dark-adapted, blues appear br ighter than reds (the ‘Purkinje shift’). Perceived br ightness also var ies with the intensity of the light in the surrounding area. The darker the surrounding area, the brighter the inner area appears (‘brightness contrast’).

Turning mechanical energy into experienced sound

Like the eye, the ear has extraordinary sensitivity. The smallest disturbance in the air that can be heard as a sound produces a pressure at the eardrum of around 0.0002 dyne/cm (at a frequency of 1 kHz). The movement this produces in the eardrum is minute—around one-tenth the diameter of a hydrogen atom! (see Green, 1976). The range of stimulus intensities that the ear can handle is even more impressive than that of the eye. The largest stimulus (around 140 decibels at the threshold of pain) is about 100,000,000,000,000 times greater than the smallest detectable stimulus. As with the eye, the range of frequencies that the ear can detect is very limited. The signals produced by insects and other animals for the purposes of communication and navigation, for example, vary in frequency from around 200 Hz to 200,000 Hz, but our ears are tuned to detect only those in the lower frequencies—from around 200 Hz to 20,000 Hz.

Even for simple dimensions of experience such as the loudness of a sound, the mapping of events as exper ienced onto the same events as descr ibed by physics is a complex one. As with light, the mapping of intensity of sound (at a given frequency) into perceived loudness follows a power function. For example, to double judged loudness one has to increase sound pressure by a factor of 10 (by around 10 decibels).3 _{Perceived loudness} of a pure tone of a given intensity also varies with frequency, increasing in loudness as frequency increases from 1 kHz to 4 kHz and decreasing in loudness from 4 kHz to 10 kHz.

Colour and pitch

Changes in the frequency of electromagnetic waves are translated by the visual system into changes in colour, and changes in the frequency of pressure waves in the air are translated into changes in pitch. The differences between seen colour and heard pitch are obvious. But there are also subtler differences in the way sensory and perceptual systems translate such frequency changes into dimensions

of experience. As the frequency of pressure variation at the eardrum increases, their perceived pitch also tends to increase, and these perceived changes can be ranked on an ordinal scale that preserves order relations (lower versus higher pitch). By contrast, if the frequency of the electromagnetic waves detected by the eye increases, the perceived colour changes from deep red, through orange, yellow, green and blue to violet. But it does not make sense to speak of violet being a ‘higher’ colour than deep red. Rather, the colour spectrum has the properties of a nominal scale, where perceived changes can be categorised and named, but not ranked (into lower versus higher).

It is also worth noting that detectable changes in the loudness and pitch of sound or the brightness and colour of light are complex transforms of the measurable changes in their intensity and frequency. For the dimensions of loudness and brightness, the minimal difference in stimulus intensity that is just noticeable is, as a first approximation, described by Weber’s law, i.e. by the equation ∂I/I = C (where I is the intensity of the stimulus, ∂I is the change in intensity which is just noticeable, and C is a constant for a given dimension of experience).4 _{This states that the minimal detectable change in intensity is a} constant proportion of the intensity to be changed (if the intensity increases, the change in intensity required to produce a just noticeable difference also increases). In the case of brightness, C is roughly 1/100, whereas for loudness C is roughly 1/5. Thus, adding one candle to one hundred other candles in a darkened room may just make a noticeable difference in brightness, but adding the noise of one machine to the noise of a hundred similar machines makes no difference in perceived loudness at all (one would need to add around twenty machines to make a difference).

The change in sound frequency required to produce a just noticeable change in perceived pitch, on the other hand, follows a somewhat different pattern. Below 1 kHz the minimal discriminable change in frequency is roughly constant; every time the frequency changes by about 3 Hz one can hear a change in pitch. Above 1 kHz Weber’s law seems to apply: the greater the frequency, the greater the change in frequency needs to be before it is heard as a change in pitch. For visible light, the change in frequency required to produce a just noticeable difference in the hue of a colour is described by a W-shaped curve—a very different relationship again.

How sensory systems translate energies into experiences

Our sensory systems provide us with dimensions of experience which model the energies surrounding our bodies. However, even for simple dimensions of experience such as brightness, loudness, pitch and colour, the mapping of what is experienced onto what physics describes is a complex one. Our eyes, ears and other sense organs are not general-purpose sound-level meters, frequency analysers and so on. They are energy detectors of a very specialised kind. The perceptual processes that operate on their output, furthermore, do so in a very

specialised way. Needless to say, when more complex aspects of perception are taken into account such as the effects of adaptation, context and expectation (based on prior experience), the relation of what is perceived to the simple measurements that meter readings provide becomes even more remote. Studies with the sensory-impaired, and experiments with systems that alter the normal translation of energies described by physics into events as experienced, also make it clear that there is considerable variation in the phenomenal worlds that can, potentially, be experienced by humans.

Experienced worlds with bits missing

To those with red—green colour blindness, traffic lights do not change colour as they change from ‘stop’ to ‘go’; only a change in the relative brightness of the top and bottom lights is seen. For the sensory-neural deaf with hearing only in the low frequency ranges (say below 1 kHz), many environmental sounds, and sounds of speech, cannot be heard. Gas does not ‘hiss’, the rain does not ‘spatter’, doorbells do not ‘ring’ and the words sue, shoe, chew, zoo and tr ue all sound like ‘ooh’. Amoore (1977) has listed seventy-six ‘anosmias’—specific smells to which one may be ‘blind’. There are those who cannot smell the odour of cloves, those who cannot smell mint, others who cannot smell garlic, and so on. Some individuals live in a world that has no pain. Those who suffer from this congenital insensitivity provide convincing testimony on the value of pain:

Many of these people sustain extensive burns, bruises and lacerations during childhood, frequently bite deep into the tongue while chewing food, and learn only with difficulty to avoid inflicting severe wounds on themselves. The failure to feel pain after a ruptured appendix, which is normally accompanied by severe abdominal pain, led to near death in one such man. Another man walked on a leg with a cracked bone until it broke completely.

(Melzak, 1973, p. 15)

The world of the congenitally blind

As the severity of the impairment increases, the experienced change in what is taken to be the ‘normal’ world may be profound. Not only are there experiential elements missing, but the functions of impaired senses may also be taken over by remaining ones. Once this happens, the world that is manifest in perception, imager y or imag ination, or symbolised in experienced thoughts, may be of a very different kind. For example, objects in the form that we know them do not exist for the congenitally blind. Their objects have no visible shape or colour in perception, memory or imagination. Object shape is known only in ter ms of how it feels. Not

surprisingly, if vision is suddenly restored by a cataract operation or by a corneal graft, such people may at first find it impossible to identify even simple shapes like triangles and squares by sight alone, although by touch they identify these with ease. Visual identification may also be very difficult to learn. Von Senden (1932), in a review of such cases, notes that one patient was trained to discriminate a triangle from a square over a period of thirteen days but could still not ‘report their form without counting corners one after the other’. Even if patients do learn to identify an object promptly, seemingly tr ivial changes in the nature of the object may destroy recognition. For example, Hebb reports that

The patient who had learned to name a ring showed no recognition of a slightly different ring; having learned to name a square, made of white cardboard, could not name it when its color was changed to yellow by turning the cardboard over; and so on.

(Hebb, 1949, p. 28) What kind of world is it that the blind inhabit? Sheila Hocken, who has made the journey both into and out of blindness, describes it with eloquence:

I had no idea that I could not see normally until I was about seven. I lived among vague images and colours that were blurred, as if a gauze was over them. But I thought that was how everybody else saw the world. My sight gradually became worse and worse until by my late teens, I could just about distinguish light from dark, but that was all. Even in my dreams the people had no faces. They were shapes in a fog. From my earliest recollection, waking or dreaming, the fog had always been there, and it slowly closed in until it became impenetrable and even the blurred shapes finally disappeared.

(Hocken, 1977, p. 1) Her memories of her childhood contained no images of her mother and father ‘except in terms of touch and sound’; she remembered the house she lived in ‘by the smell of bread baking and pies cooking, and the warmth and sound of a coal fire crackling and hissing in the grate. But no more’ (ibid., p. 2).

Her blindness resulted from congenital cataracts with attendant retinal deterioration. However, when at the age of 30 an operation was performed to restore the transparency of the lens, her visual world was born anew:

What happened then—the only way I can describe the sensation—is that I was suddenly hit, physically struck by brilliance, and through my entire body. It flooded my whole being with a shock-wave, this utterly unimaginable, incandescent brightness: there was white in front of me,

a dazzling white that I could hardly bear to take in, and a vivid blue that I had never thought possible. It was fantastic, marvellous, incredible. It was like the beginning of the world.

(ibid., p. 148) After a few days she leaves the hospital and is amazed by the way the world that now surrounds her differs from the one that she has previously taken for granted as being ‘real’. She is surprised, for example, by the trees:

Of course I knew there were trees. I’d always been aware of them, and could hear them when the wind blew. But I have never imagined so many, or that they were everywhere, growing out of pavements, in gardens and, as we drove through the countryside towards Nottingham, more and more of them, all different shapes. I could not get over the shapes, some round, some tall, and all in varying, breathtaking shades of green.

(ibid., p. 160) Like von Senden’s patients she initially found it difficult to relate some of the images she could see to her prior ‘reality’ which depended on touch. At the greengrocer’s, for example,

There was something on the counter that I could not, try as I would, put a name to. I could see some red, and green, and a shape. That was all it meant to me. It would not fit any description I could think of. Then I touched it. I realised I was seeing leaves and flowers. It was a plant. I could not understand why I had not immediately known what it was.

(ibid., p. 168) For her, a childhood ‘reality’ constructed from what is felt and heard, that she can smell and taste but cannot see, has now been reconstructed and must be re- cognised in a visual form.

The world of the deaf

To those who previously had hearing, the loss of auditory sensation is traumatic and, in some ways, surprising in its effects. As D.A.Ramsdell points out, sound not only serves to communicate our verbal thoughts, but also forms an auditory background to all of daily living:

We react to such sounds as the tick of a clock, the distant roar of traffic, vague echoes of people moving in other rooms in the house, without being aware that we do hear them. These incidental noises maintain our

feeling of being part of a living world and contribute to our sense of being alive. We are not conscious of the important role which these background sounds play in our comfortable merging of ourselves with the life around us, because we are not aware that we hear them. Nor is the deaf man aware that he has lost these sounds; he only knows that he feels as if the world were dead.

(Ramsdell, 1947, p. 395) The English politician Jack Ashley describes his final loss of hearing with sadness:

I was cut off from mankind, surrounded by an impenetrable barrier. I could see people clearly, but they belonged to a different world—a world of talk, of music and laughter. I could hardly believe I would never hear again. I tried pressing a radio to the side of my head in a vain attempt to make contact; when I turned the volume to full pitch I could only feel a delicate vibration as the set trembled. It was undeniable confirmation that although sound existed it was not for