Pathology Based Philosophy of Mind

Dr Craig French–Postdoctoral Research Fellow on the John Templeton Foundation’s New Directions in the Study of Mind Project in the Faculty of Philosophy, University of Cambridge and Research Fellow, Trinity Hall, University of Cambridge,

 

Is all vis­ion col­our vis­ion? What about in type 2 blind­sight where there is lim­ited con­scious­ness of move­ment and form without col­our? Does see­ing an object require see­ing it as spa­tially loc­ated and see­ing some of the space it occu­pies? What about in Bálint’s Syndrome when at any giv­en time a single object and noth­ing else is seen? How can such patho­lo­gies inform our the­or­iz­ing about men­tal phe­nom­ena such as vision?

Pathology based philo­sophy of mind can take neg­at­ive and pos­it­ive forms. On the neg­at­ive side, reflec­tion upon patho­lo­gic­al con­di­tions can give us empir­ic­al counter­examples. We start by high­light­ing a core claim involved in a philo­soph­ic­al the­ory of some men­tal phe­nomen­on, for instance, a claim about the nature of thought, or con­scious­ness, or per­cep­tion, or whatever. But then we look to a patho­lo­gic­al case, where we find the phe­nomen­on in ques­tion, but in such a form that the ini­tial claim can­not be sus­tained. However, such reflec­tion doesn’t have to take this neg­at­ive form. It may force us to recon­sider the start­ing claim. But this might instead prompt an attempt to artic­u­late a more subtle ver­sion of it. Looked at in this way, reflec­tion upon the patho­logy can play a pos­it­ive role, it can help us to devel­op and fin­esse philo­soph­ic­al theories.

Thus, patho­logy based philo­sophy of mind can be fruit­ful in dif­fer­ent ways. And the sig­ni­fic­ance of such work is not con­fined to philo­sophy. For it might also yield inter­est­ing per­spect­ives on patho­lo­gies themselves.

An excel­lent example of patho­logy based philo­sophy of mind is to be found in Fiona Macpherson’s “The Structure of Experience, the Nature of the Visual, and Type 2 Blindsight”. Macpherson con­siders a tra­di­tion­al claim in the philo­sophy of per­cep­tion: the claim that all vis­ion is col­our vis­ion. Call this the Colour Claim. This claim is as old as Aristotle and his claim that col­our is the prop­er object of sight. And it does seem plaus­ible. Although vari­ous forms of col­our blind­ness are pos­sible, these are typ­ic­ally cases in which col­our vis­ion is severely degraded, not cases of visu­al exper­i­ence without any exper­i­ence of col­our (includ­ing achromat­ic col­ours). And for many of us it will be very dif­fi­cult to ima­gine a visu­al exper­i­ence which is not a col­our exper­i­ence. Moreover, the Colour Claim earns its the­or­et­ic­al keep. Combined with the idea that only visu­al exper­i­ences are col­our exper­i­ences, we can use it to explain what dis­tin­guishes vis­ion from oth­er senses.

What does Macpherson have to say about the Colour Claim, and what has it got to do with patho­logy based philo­sophy of mind? Though she doesn’t frame her dis­cus­sion in quite this way, Macpherson effect­ively argues that the Colour Claim comes under pres­sure from a cer­tain patho­lo­gic­al con­di­tion: type 2 blind­sight. When we look to the form that visu­al exper­i­ence takes in a cer­tain sort of patho­lo­gic­al case – type 2 blind­sight – we see that the Colour Claim is unsus­tain­able (if, that is, we accept the con­cep­tion of type 2 blind­sight, which Macpherson argues is defens­ible, and on which it involves visu­al exper­i­ence). Let me briefly spell out some of the details of Macpherson’s discussion.

The phe­nomen­on of blind­sight involves a puzz­ling com­bin­a­tion of con­di­tions. On the one hand, a sub­ject with blind­sight seems to lack con­scious exper­i­ence of stim­uli presen­ted in a cer­tain por­tion of their visu­al field. Such sub­jects report that they are blind in that area of the visu­al field – the area thus gets called the blind field. On the oth­er hand, such sub­jects are remark­ably accur­ate at determ­in­ing the pres­ence of stim­uli and cer­tain fea­tures presen­ted in the blind field, when forced to guess in exper­i­ment­al con­di­tions (Weiskrantz (2009)).

Now it turns out that some indi­vidu­als with blind­sight have lim­ited con­scious­ness in their blind fields. Thus, Weiskrantz (1998) intro­duced a dis­tinc­tion between type 1 and type 2 blind­sight. The former type is as described above, the lat­ter encom­passes cases where there is lim­ited con­scious­ness in the blind field. In what way is the con­scious­ness involved in type 2 blind­sight lim­ited? It is lim­ited in involving con­scious­ness of just move­ment and form. (More care­fully: a plaus­ible under­stand­ing of the con­scious­ness of one type 2 blind­sight patient – GY – is that he has con­scious­ness of just move­ment and form (Macpherson, p. 115). Other cases may dif­fer, but we can take this as a model).

The ques­tion Macpherson con­siders is how are we to under­stand such con­scious­ness. Should we under­stand it as visu­al exper­i­ence? As con­scious thought? As con­scious feel­ing? Or some­how else? Suppose we under­stand it as visu­al exper­i­ence. Well, then we have a patho­logy based counter­example to the Colour Claim. Since the con­scious­ness involved in type 2 blind­sight is con­scious­ness of just move­ment and form, such visu­al exper­i­ence would have to be visu­al exper­i­ence of just move­ment and form, and so visu­al exper­i­ence without col­our exper­i­ence. It is, as Macpherson brings out, a mat­ter of hot debate wheth­er the con­scious­ness involved in type 2 blind­sight should be under­stood as visu­al exper­i­ence. But Macpherson defends the idea that the con­scious­ness involved in type 2 blind­sight can be under­stood as visu­al exper­i­ence (without pre­tend­ing to offer a decis­ive case for this). Thus what we effect­ively get are (defeas­ible) grounds for the claim that type 2 blind­sight is a patho­logy based counter­example to the Colour Claim.

Macpherson’s work is a par­tic­u­larly excel­lent example of patho­logy based philo­sophy of mind. Not only does it advance a philo­soph­ic­al issue (the status of the Colour Claim), it fur­thers our under­stand­ing of a patho­lo­gic­al con­di­tion itself (type 2 blindsight).
Some of my own work – “Bálint’s Syndrome and the Structure of Experience” – falls into the mould of patho­logy based philo­sophy of mind. One tra­di­tion­al philo­soph­ic­al claim about see­ing an object is that it must involve (a) see­ing the object as spa­tially loc­ated, and (b) see­ing some of the space occu­pied by the object. I call this the spa­tial per­cep­tion require­ment (SPR). (There is instruct­ive dis­cus­sion of some such require­ment and how it finds sup­port in Kant, Husserl, and Wittgenstein in Schwenkler (2012)).

(SPR) comes under pres­sure from Bálint’s Syndrome – a patho­lo­gic­al spa­tial per­cep­tu­al dis­order defined in terms of three main defi­cits: sim­ul­tanagnosia, optic atax­ia, and optic aprax­ia. Simultanagnosia is the inab­il­ity to see more than one object sim­ul­tan­eously, optic atax­ia is an inab­il­ity to reach accur­ately for seen objects, and optic aprax­ia is a con­di­tion whereby gaze remains fix­ated des­pite a lack of a prob­lem with eye move­ment. A strik­ing illus­tra­tion of the first two defi­cits can be found here:

The pres­sure to (SPR) comes from the dom­in­ant inter­pret­a­tion of Bálint’s Syndrome on which sub­jects can see objects (though only one at a time) yet can­not see either space or spa­tial loc­a­tion. The dom­in­ant inter­pret­a­tion has it that Bálint’s Syndrome is a rad­ic­al form of spa­tial blind­ness. Lynn Robertson and col­leagues have extens­ively tested a patient with Bálint’s Syndrome, RM, and their find­ings sup­port this inter­pret­a­tion. Thus, they describe Bálint’s Syndrome and its mani­fest­a­tion in RM as follows:

These patients per­ceive a single object… yet they have no idea where it is loc­ated. It is not mis­lo­cated. Instead it seems to have no pos­i­tion at all (2004, p. 108)… During early test­ing of his [RM’s] extraper­son­al spa­tial abil­it­ies he often made state­ments like, “See, that’s my prob­lem. I can’t see where it is.”… objects that popped into his view were not mis­lo­cated per se. Rather, they simply had no loc­a­tion in his per­cep­tu­al exper­i­ence (pp. 158–159)… RM had… com­pletely lost his abil­ity expli­citly to rep­res­ent space (1997, p. 302).

A defend­er of (SPR) might be temp­ted to claim that RM just doesn’t see objects. But this is empir­ic­ally implaus­ible, as argued con­vin­cingly by Schwenkler. Not only can RM see (and identi­fy) objects, he can see them as coher­ent wholes, as hav­ing shape, size, and col­our (though his col­our per­cep­tion is often erro­neous, as emphas­ized in Campbell (2007)).

What I argue, how­ever, is that Bálint’s Syndrome doesn’t give a counter­example to (SPR) (see §4 of my paper). Instead, it helps us to see how some­times see­ing objects involves only very lim­ited space and spa­tial loc­a­tion awareness.

There are two aspects to my dis­cus­sion on this point. First, I argue that the evid­ence doesn’t rule out that indi­vidu­als with Bálint’s Syndrome are cap­able of a severely lim­ited form of loc­a­tion aware­ness. The empir­ic­al evid­ence points to vari­ous prob­lems with ego­centric and allo­centric loc­a­tion aware­ness – see­ing objects as loc­ated rel­at­ive to one­self and oth­er things. But it doesn’t rule out purely object-centric loc­a­tion aware­ness; see­ing an object as there where ‘there’ picks out just the space occu­pied by and defined in terms of the bound­ar­ies of whatever object is seen.

Second, I argue that the idea that indi­vidu­als with Bálint’s Syndrome can see space is empir­ic­ally con­sist­ent. Again, such space per­cep­tion would have to be severely lim­ited: con­fined to just object-space. Bálint’s patients may not be able to see the object-space as a space in a lar­ger region of space, nor will their per­cep­tion of such space be inde­pend­ent of and dis­so­ci­able from their per­cep­tion of the object (as it might be for us when we see a fig­ure as upside down, where its top points to the bot­tom of the space in which it’s seen), but, for all that, they can still clap their eyes upon regions of space delim­ited by the objects they see. I argue fur­ther that we have pos­it­ive reas­on to sup­pose that Bálint’s patients do see object-spaces. RM, for instance, can see objects as shaped and exten­ded. He can thus see objects as tak­ing form in and extend­ing into space – as occupy­ing space. This sug­gests that he can see the object-spaces of the objects he sees.

If I am right, we can res­ist the idea that in Bálint’s Syndrome visu­al aware­ness of space and spa­tial loc­a­tion goes miss­ing. In the final sec­tion of my paper I sug­gest, instead, that we can char­ac­ter­ize the exper­i­ences of those with Bálint’s Syndrome in terms of the idea that the visu­al field goes miss­ing (on the par­tic­u­lar con­cep­tion of the visu­al field we find in Martin (1992, 1993), Richardson (2010), and Soteriou (2013), see also Mac Cumhaill (2015)).

The visu­al field involved in ordin­ary visu­al exper­i­ence delim­its a cone of phys­ic­al space, which we are aware of, and in which things are seen as loc­ated, in rela­tion to one­self, and oth­er things (includ­ing regions space). Such exper­i­ence is lim­ited, and its lim­its can be spe­cified in terms of the bound­ar­ies of the space delim­ited by the visu­al field: the bound­ar­ies seem to be bound­ar­ies bey­ond which things can’t now be seen. But they seem to be bound­ar­ies bey­ond which things could be seen, if one alters one’s point of view. As Richardson and Soteriou emphas­ize, such lim­its come not from any object or space one per­ceives, but are rather mani­fest­a­tions of one’s own sens­ory lim­it­a­tions. Thus a change in the lim­it­a­tion strikes one as a change in one’s own sens­ory lim­it­a­tions, and not as a change in any object or space in the world (as presen­ted in exper­i­ence). Suppose I gradu­ally come to have a nar­row­er field of view. The way in which my exper­i­ence is lim­ited thus changes: it becomes more lim­ited. Before the change, the lim­it­a­tion was to a region of space of such-and-such a size, but now it is to a region of space of a smal­ler size. In reflec­tion upon my exper­i­ence, this strikes me as a change in my sens­ory lim­it­a­tions, not as change in the (presen­ted) world, as the shrink­ing of some object or space.

Now even if the exper­i­ences of Bálint’s patients involve aware­ness of space and spa­tial loc­a­tion, they are noth­ing like this. Suppose RM sees an apple in apple-space. RM can be aware only of what falls with­in the apple-space he sees. But this lim­it­a­tion is set by the apple he sees, and its spa­tial struc­ture. If RM goes from being aware of the apple, to being aware of, say, a church, or a banana, the way in which his exper­i­ence is lim­ited will change accord­ingly. The spa­tial spe­cific­a­tion of the lim­it­a­tion will now be set by the spa­tial struc­ture of the church or the banana. The spa­tial struc­ture of RM’s exper­i­ence is behold­en to whichever object he hap­pens to see and this is quite unlike how things are in exper­i­ences which involve a visu­al field.

 

REFERENCES

Campbell, John (2007). “What’s the role of spa­tial aware­ness in visu­al per­cep­tion of objects?” Mind and Language 22.5, pp. 548–562.

French, Craig (2015). “Bálint’s Syndrome and the Structure of Visual Experience”. Unpublished Manuscript. http://craigafrench.github.io/assets/CFBalintsPaper.pdf

Mac Cumhaill, Clare (2015). “Perceiving Immaterial Paths”. In: Philosophy and Phenomenological Research 90.3, pp. 687–715.

Macpherson, Fiona (2015). “The Structure of Experience, the Nature of the Visual, and Type 2 Blindsight”. In: Consciousness and Cognition 32, pp. 104–128.

Martin, Michael G. F. (1992). “Sight and Touch”. In: The Contents of Experience. Ed. by Tim Crane. Cambridge: Cambridge University Press, pp. 196–215.

— (1993). “Sense Modalities and Spatial Properties”. In: Spatial Representation: Problems in Philosophy and Psychology. Ed. by Naomi Eilan, Rosaleen McCarthy, and Bill Brewer. Oxford: Oxford University Press, pp. 206–217.

Richardson, Louise (2010). “Seeing Empty Space”. In: European Journal of Philosophy 18.2, pp. 227–243.

Robertson, Lynn (2004). Space, Objects, Minds and Brains. Hove, East Sussex: Psychology Press.

Robertson, Lynn et al. (1997). “The Interaction of Spatial and Object Pathways: Evidence from Balint’s Syndrome”. In: The Journal of Cognitive Neuroscience 9.3, pp. 295–317.

Schwenkler, John (2012). “Does Visual Spatial Awareness Require the Visual Awareness of Space?” In: Mind and Language 27.3, pp. 308–329.

Soteriou, Matthew (2013). The Mind’s Construction: The Ontology of Mind and Mental Action. Oxford: Oxford University Press.

Weiskrantz, Lawrence (1998). Blindsight: A Case Study and Implications. Paperback Edition. Oxford: Oxford University Press.

— (2009). Blindsight: a case study span­ning 35 years and new devel­op­ments. Oxford: Oxford University Press.