Psychological arguments

In psychological terms, what is at stake is the possibility of an empirical dis-tinction betweenperceptionandcognition. The empirical impetus for this view

came from the so-called ‘New Look’ school in the perceptual psychology of the 1950s. Jerome Bruner and his scholars performed a series of experiments aim-ing to show that one’s background theories influence perception. As Gilman (1992: 293) indicates, Bruneret al. (1951) assumed that perception is a three-stage process: (1) an organism has a ‘hypothesis’ about its environment; (2) the organism receives an ‘input of stimulus information’; (3) the hypothesis is confirmed or disconfirmed in view of the received information. A hypothesis thus confirmed constitutes aperception.

From these assumptions, New Look psychologists derived the following theorem:

The smaller the quantity of appropriate information, the greater the prob-ability of an established initial hypothesis being confirmed, even if en-vironmental events fail to agree with such hypotheses. (Bruner et al.

1951: 218)

Support for this statement was at first taken from Bruner’s experiments on color perception. Two decades later, Albert Hastorf studied “The Influence of Suggestion on the Relationship Between the Stimulus Size and Perceived Distance” (1970). If correct, the results of these experiments imply that sup-porters of different theories literally perceive different things, so that there is no way to have a theory-neutral observation. The conclusion was taken to under-gird Kuhnian relativism, with its known claims about the incommensurability of paradigms and the irrationality of theory choice.

However, the findings of New Look psychology have been subject to strong criticism. Gilman (1992), for example, argues that the experiments of the New Lookers are questionable both from the standpoint of their design and from the interpretation of their data. He shows that all their findings can just as easily be explained by the simpler and more plausible hypothesis that theory-dependence was manifest only at the level of (linguistically) reporting the results, with no implication about a theory-dependence of perception. Be-sides, as Gilman suggests, it is inappropriate to draw dramatic philosophical conclusions from such a shaky empirical basis.

Fodor makes a persuasive case for the claim that perception does in fact remain unaffected by background beliefs. In discussing the optical illusion produced by the M¨uller-Lyer figures, he points out that despite the fact that we have a theoretical explanation of how the illusion is produced, it doesn’t vanish:

The M¨uller-Lyer illusion is afamiliar illusion; the news has pretty well gotten around by now. So, it’s part of the “background theory” of any-body who lives in this culture and is at all into pop psychology that

displays [of the M¨uller-Lyer illusion] are in fact misleading and that it always turns out, on measurement, that the center lines of the arrows are the same length. Query: Why isn’t perception penetrated by THAT piece of background theory? ...This sort of consideration doesn’t make it seem at all as though perception is, as it’s often said, saturated with cognition through and through. On the contrary, it suggests just the reverse: that how the world looks can be peculiarly unaffected by how one knows it to be. (Fodor 1984: 34)

This is a point which Fodor generalizes for all known perceptual illusions:

To the best of my knowledge, all standard perceptual illusions exhibit this curiously refractory character: knowing that they are illusions doesn’t make them go away. (Fodor 1984: 34)

Therefore, as Fodor concludes, these facts show that perception is not influ-enced by background theory. In terms of his theory, perception is “informa-tionally encapsulated”. To understand what that means, let us take a brief look at his modular theory of perception. Sensory stimulations go to a percep-tual module P, whose operation mode is innately specified. Next, the output ofP goes to the central systemC, which is stocked with concepts and theories.

Finally, the output of C is composed of beliefs – or statements in Mentalese, the language of mind. The details of the structure of these modules are not of interest here. Two elements are relevant for the debate: first, the perceptual module P isencapsulated: only a restricted range of information is capable of influencing the output of perceptual processes. Second, the operation modes of these modules are endogenously specified. The encapsulation of perceptual modules entails that

bodies of theory that are inaccessible to the modulesdo not affect the way the perceiver sees the world. Specifically, perceivers who differ profoundly in their background theories – scientists with quite different axes to grind, for example – might nevertheless see the world in exactly the same way, so long as the bodies of theory that they disagree about are inaccessible to their perceptual mechanisms. (Fodor 1983: 38)

Fodor does not maintain that perception is not influenced at all by cogni-tion. Some terminological care is required in order to understand properly his position. He relies on a distinction between ‘sensation’ and ‘perception’. Fodor explicitly admits that there is a lot of problem-solving involved in perception.

However, he disagrees with Kuhn and Churchland about how close to the pri-mary level of sensorial input problem-solving begins, and about how susceptible to modification the problem solving mechanisms are. Kuhn (1962/1970), for example, suggests that theory is involved at the fundamental level of sensory

perception and that new theories alter perception radically. There is accord-ing to him, no perceptual moduleP. Yet as Gilman (1992) remarks, Kuhn’s psychological vocabulary differs from the standardized one:

First, ‘stimuli’ are identified with the impressions taken by sensory appa-ratus and not with external physical causes of those impressions. Second,

‘sensations’ are not merely stimuli transduced, but stimuli that have been processed in some determinate fashion. Stimuli cannot be subjected to

‘awareness’, but ‘sensations’ can. Note: there does not seem to be a sen-sation/perception distinction here; that is, it seems that ‘sensation’ and

‘perception’ are used interchangeably. (Gilman 1992: 293)

Kuhn apparently settles a good deal of the issue not through argumentation, but on a terminological basis. Yet, we ought to note that Gilman’ terminol-ogy draws itself upon the assumptions of the theory in which it is embedded.

Gilman calls ‘stimulus’ the external cause of perception, and ‘sensations’ the output of sensory transducers. All right thus far. But he then defines ‘percep-tion’ as the output of perceptual modules, thus presupposing the correctness of the modularity theory (see Gilman 1992: 293).

A strong criticism directed against Fodor’s theory has been levelled by Churchland (1988). Churchland proceeds in two steps: first, he challenges the correctness of several fundamental claims of the modularity theory. Second, assuming for the sake of the argument that it were right, he sets out to show that modularity cannot entail the theory-neutrality sought by Fodor. Let us take these two objections in turn.

Network vs. modular theories of perception

Churchland (1988) claims that there is enough experimental evidence to show that optical perception can be diachronically modified. He draws on this evi-dence to support his network theory of perception.

Churchland mainly turns to inverted lenses experiments. If one puts on spectacles which invert the retinal image, one will first have difficulties in getting around. After about a week, one starts reorienting oneself in the visual field. After removing the spectacles, another few days are needed for one to return to the original state. This fact is enough, as Churchland maintains, to elucidate the plasticity of visual perception. However, Fodor denies that inverting lenses experiments in any way boost the idea of a theory-penetrability of vision. All that it is shown, Fodor suggests, is that visual-motor skills can be ‘re-calibrated’ by a process of learning. Therefore, as Fodor claims, there is no proof of the theory-penetrability of perceptual modules.

Next, Churchland cites neurological evidence in support of his network theory of perception. He claims to have identified ‘descending pathways’ whose existence is taken to indicate that

the wiring of the brain relative to its sensory periphery certainly does not suggest the encapsulation and isolation of perceptual processing. As with the psychological data discussed earlier, it strongly suggest the opposite arrangement. (Churchland 1988: 178)

Two methods of charting these neural descending pathways are cited: extra-cellular dye injection, and monitoring of the path or radioactive amino acids.

Churchland also cites several studies conducted on birds and on human sub-jects.

Nevertheless, Gilman attacks every piece of evidence that Churchland has brought forward. Gilman denies the relevance of the cited studies, on grounds of the peculiarities of the subjects. He also dismisses the conclusions that Churchland has drawn from studies on the efferent pathways. The materials cited by Churchland, he continues, do not undergird the “downward penetra-tion of theories or beliefs.” (Gilman 1992: 302).

Churchland also reiterates the discussion of optical illusions, adding new examples (e.g. the Kanisza illusion). But Fodor is little impressed by this new case. He maintains that the descriptions of the procedures needed in order to wipe out some of the illusions do not support the claim that theory penetrates perception:

One doesn’t get the duck/rabbit (or the Necker cube) to flip by “changing one’s assumptions”; one does it by (for example) changing one’s fixation point. (Fodor 1988: 190)

More recent evidence in favor of the impenetrability of the visual system by theoretical and cultural influences is put forth by Gilman (1994). He discusses Goodman’s (1976) argument claiming that natural resemblance accounts of vision fail because there is no principled basis on which to establish what aspect of a scene, and to what degree of detail, is to be copied when we want to represent it. Gilman’s retort is that both a physiological and a computational analysis of the visual system converge at showing that a representation worth its name copies

those aspects of a scene which fix the geometry of light/dark contrasts to a degree when presented with the picture as it would when presented with the original scene. (Gilman 1994: 95)

All in all, this is an intricate empirical debate, and we are not in a position to draw any definite conclusion as to the winning part. However, it is fairly

safe to state that Churchland has not conclusively shown the modular theory to be false. In any event, Churchland is willing to grant, for the sake of the argument, that perception is encapsulated. From this it does not follow, he maintains, that observation is theory-neutral. This is the most interesting part of the debate.

Theory neutrality or universal dogmatism?

In a sense, Fodor admits that perception is partly determined by background information. The reason is that, “as a matter of principle, any given pattern of proximal stimulation is compatible with a great variety of distal causes”

(Fodor 1984: 30). In other words, perceptual outputs should, in absence of sup-plementary information, be underdetermined by sensory inputs. But, Fodor maintains, they are not so underdetermined. Thus, the questions

How is it possible that perception should ever manage to beunivocal (to say nothing ofveridical)? Why, that is, doesn’t the world look to be many ways ambiguous, with one “reading” of the ambiguity corresponding to each distal layout that is compatible with the current sensory excitation?

(Fodor 1984: 31)

can be responded to only by accepting that background information plays a role in perceptual processes. As we have mentioned, according to modular theory, this information is of an innate kind. Perceptual modules are not penetrable by all background knowledge, and by no means by information descending from the central system. The information influencing perception is endogenously specified.

Churchland raises the following objection: assuming that perception is governed only by endogenously specified information, what follows is that per-ception has features common in all humans, not that human perper-ception is objective. As Churchland states,

Let us suppose ... that our perceptual modules ... embody a systematic set of ... assumptions about the world, whose influence on perceptual processing is unaffected by further or contrary information.... This may be a recipe for a certain limited consensus among human perceivers, but it is hardly a recipe for theoretical neutrality... What we have is a universal dogmatism, not an innocent Eden of objectivity. (Churchland 1988: 169–170)

I believe that this objection sounds more threatening than it actually is. The reason is that the “limited consensus” which Churchland derisively grants is sufficient to support the argument against incommensurability. If the mod-ularity theory is correct about the endogenously specified knowledge being

common to humans, there is then, as Kukla (1998: 117) indicates, a one-to-one mapping between the sensory input and the perceptual output; there is a mode of perception common to all human beings, regardless of their cultural and theoretical background. It must be admitted that this is a strong conclu-sion. It entails that an observational language can be built on that perceptual consensus.

Kukla’s irrelevance objection

Kukla (1998) raises a very interesting objection against the modularity the-ory. He argues that, whether true or false, Fodor’s theory is ineffective in the incommensurability issue. Kukla suggests that our epistemological situa-tion does not depend on whether we perceive the world through encapsulated modules or through theory-penetrated modules.

A few terminological preliminaries are in order before discussing Kukla’s objection. Adversaries of modularity theory maintain that there are direct links between the sensory transducers and the central system. Thus, “the acquired theories can contribute to the operations of assembled (i.e., not hardwired and not innate) perceptual systems (henceforth APs)...” (Kukla 1998: 119). The notion of anassembled perceptual system (AP) can be used to construct variants of the modularity theory different from – or even opposed to – Fodor’s theory. Here are some models:

(a) The central system C gets direct inputs from the sensory transducers, inputs which bypass the endogenous perceptual moduleP. Thus, C has information available from both P and the acquiredAPs.

(b) C has a top-down control overP – as Churchland seems to maintain.

(c) There is no P at all – as Kuhn seems to maintain. The outputs of APs comprise all the perceptual information available to C.

As with Kukla (1998: 119), let us call (a) the mixed model. Thus, the list of modular models to discuss is as follows: Fodor’s model of encapsulated modules, the mixed model (a), Churchland’s model (b), and Kuhn’s model (c).

Not surprisingly, Fodor and Gilman reject the notion of an assembled per-ceptual system. Gilman argues that there is no reason to posit the existence of APs in the first place, since one can account for the outcome of the perceptual system in terms of the innate perceptual moduleP alone:

Recall the Kuhnian example of someone who “literally” sees the tracks of electrons, alpha particles, and so forth as opposed to droplets. Or the

well-known example of the scientist who always sees a pendulum as a pendulum. Surely none would deny that such people can explain what they are noticing to people not conversant with the relevant concepts (or to people who are sceptical about the evidence) by pointing to the droplets as droplets. Surely a scientist is capable of turning to a scientist’s child and saying: “look there, you see how that weight is swinging at the end of the line...” when the child says that he does not know what a pendulum is. (Gilman 1992: 307)

As Gilman’s argument goes, the physicist and the child have in fact the same perceptual experience, coded in the format of P. The difference in compe-tence between them then would originate in the compecompe-tence of employing a theoretical language founded on the observational language.

This reasoning of Gilman is not conclusive. The reason is that the ex-istence of APs would in no respect alter the picture described in the latter quote. As long as both the physicist and the child own identical perceptual modulesP, they share a common body of perceptions, regardless of whether the two also have assembled perceptual systems or not. As Kukla puts it, “we enjoy the befits of an endogenously specifiedP in additionto assembledAPs.”

(1998: 120). On the basis of that common perception, a neutral observational language can be built. This observation language could then serve as a trans-lation basis for different theoretical approaches, thus precluding any threat of incommensurability. If these considerations are correct, it follows that Fodor and Gilman failed to show that the mixed model (a) is not in place.

Now to the examination of (b) and (c), that is, Churchland’s and Kuhn’s perceptual models. The first one claims thatP is completely controlled by the central processorC, while the latter plainly rejects P’s existence. Thus, both of these models seem to include the claim thatall observations are influenced by the theoretical background, to the effect that there is no theory-neutral observational basis. I agree with Kukla that with respect to the incommen-surability issue, (b) and (c) do not fare better than the mixed model. To see that, let us consider two scientists, S1 and S2, whose perceptual information comes only from assembled perceptual systems. Let us suppose that S₁ pos-sesses the assembled perceptual systemAP1, whileS2 does not. It follows that S2 can neither confirm, nor disconfirm the theoretical claims of S1. However, as Kukla claims,

if S1 has managed to assemble AP1, there’s no reason why S2 can’t as-semble it as well. In fact, there’s no reason why anyone can’t assemble AP1. If everyonedidassembleAP1, then the epistemic situation would be identical to the situation that results from our sharing the endogenously specified perceptual moduleP. (Kukla 1998: 121)

Assembling a relevant perceptual system may require a discouraging amount of effort to be invested – one might need, for instance, to become an expert in theoretical physics – which points to an asymmetry between having P and assembling anAP. Yet, the incommensurability due to the absence of anAP is not of an insurmountable kind. It actually has an equivalent in the situation where owners of an endogenously specified perceptual module P would, for whatever reason,fail to useP. These are both cases of remediable incommen-surability. They do not have any of the dramatic consequences announced by Kuhn, such asS₁ and S₂ “living in different worlds.”

Kukla infers that the mixed and the Kuhnian models cannot be distin-guished by their epistemological consequences. But I believe there might be a more substantial difference between possessing the innate P and assembling an AP. In the former case, P would assure at any moment a common pool of human perceptions in which epistemic agents could settle their theoretical conflicts. Hence, incommensurability would be excluded. In the latter case, AP can be assembled or disassembled – at will or involuntarily. As such, the incommensurability of any two ‘world-pictures’ would threaten to depend on the momentary psychology ofS1andS2, respectively. This, in turn, would en-gender the issue of bringing about credibility within a scientific community. It is a corollary of our discussion of the technological argument, that among hu-man scientists, such credibility negotiations are feasible. However, it dehu-mands considerable effort and time, and this allows ade facto incommensurability to threaten at any moment. By the time a concrete incommensurability situa-tion is eliminated, other cases can emerge. Not so from Fodor’s standpoint:

Kukla infers that the mixed and the Kuhnian models cannot be distin-guished by their epistemological consequences. But I believe there might be a more substantial difference between possessing the innate P and assembling an AP. In the former case, P would assure at any moment a common pool of human perceptions in which epistemic agents could settle their theoretical conflicts. Hence, incommensurability would be excluded. In the latter case, AP can be assembled or disassembled – at will or involuntarily. As such, the incommensurability of any two ‘world-pictures’ would threaten to depend on the momentary psychology ofS1andS2, respectively. This, in turn, would en-gender the issue of bringing about credibility within a scientific community. It is a corollary of our discussion of the technological argument, that among hu-man scientists, such credibility negotiations are feasible. However, it dehu-mands considerable effort and time, and this allows ade facto incommensurability to threaten at any moment. By the time a concrete incommensurability situa-tion is eliminated, other cases can emerge. Not so from Fodor’s standpoint: