Now imagine your V1 is normal, but an evil genius removes your temporal lobes (the what pathway) under anesthesia. What would the world look like when you woke up? Without the what pathway, you wouldn’t be able to recognize, name or appreciate the meanings of things around you. Yet because the how pathway is intact, you would still “see” in the sense of being able to reach out for objects, to dodge missiles hurled at you or to avoid obstacles. It is hard to imagine this scenario, but it would be roughly equivalent to being transported to the Red Planet (without your knowledge) and waking up in a gallery of Martian abstract art. You could not recognize anything or understand it but could still find your way around, copy the shapes of things and step over fallen objects. Everything around you—chairs, tables, people, cars—would look like meaningless abstract art. You would have profound visual agnosia.
This kind of complete damage is rare, but even with partial damage a condition called Klüver-Bucy may develop. In this variant of agnosia the patient has some difficulty identifying common objects but more profound agnosia for food and appropriate “sex objects.” Patients cannot discriminate food from inedible objects, so they may put pebbles in their mouth. Such people may make sexual overtures to the patient in the adjacent bed, to the doctor or even to animals, though they are mentally normal in other respects.
Seeing without Naming
John’s predicament is somewhat similar. In some ways, it is more severe because he has great difficulty identifying any object. Yet he doesn’t take this to the absurd lengths of trying to eat inedible objects or engaging in indiscriminate sexual behavior. In Klüver-Bucy patients there is probably relatively greater damage to regions in the temporal lobes concerned with sex, food and other primal urges, whereas in John the damage mainly affects regions involved in recognizing more neutral and commonplace objects such as chairs, goats and carrots.
Recall, especially, that he could copy pictures accurately, although he was unable to identify or name them. This is because his how pathway is undamaged, and it can guide the hand around to draw a faithful rendering. Without the what (temporal lobe) pathway, he does not know what it is. Amazingly, he could even use shears to trim the hedge in his garden (which only requires how) but could not weed the garden because he had lost the ability to discriminate weeds from flowers. But his problems were not quite as extreme as seen in Klüver-Bucy; he could often recognize the general category that an object belonged to (“it’s an animal”) albeit not the specific exemplar (he might say “dog” instead of the correct “goat”). Or he would identify a carrot as a paintbrush (“because it’s long and has a tuft at its end”).
And thus we can begin to explain the unusual perceptions of GY and John, by examining their particular deficits in terms of our detailed knowledge of the visual areas and their connections and evolutionary origins. In doing so, we have not only explained these bizarre symptoms but also gained new insights into how normal vision works. Contrary to naive intuition, vision is not a single process. Instead it involves multiple specialized areas working in parallel. How the outputs of these areas are combined to create a seamless unity of conscious perception, however, is as yet an unsolved mystery.
Note: This story was originally published with the title, "I See, But I Don't Know".