Late Vision

After early vision there is cognition, a stage that includes higher vi-sual and non-vivi-sual processes. This stage, that by definition is cognitive (Pylyshyn 1984, 134-135; Raftopoulos 2001a, 427; 2009a, 77, 80), is la-belled “cognition” by Pylyshyn (1999a, 344) and “observation” by Fodor (1984) and Raftopoulos (2001c, 188; 2009a, 51).

According to this interpretation, cognition is composed by late vision and cognitionproperly speaking. Late vision (or high-level vision (Hildreth and Ullman 1989)) is a stage of visual processing which requires access to memory for recognition and categorization of objects. It goes from the

19Despite this interpretation, some philosophers take the output of early vision as being perceptual experiences, e.g.,Toribio(2014, 623-626).

early visual output to the generation of the perceptual experience.²⁰ Cog-nition properly speaking refers to the highest stage of cognition responsible for doxastic, emotional or desiderative processing. This latter stage is in-dependent from perception and purely cognitive: it starts after late vision and generates mental states on the basis of perceptual experiences. On this interpretation, late vision is the lowest cognitive level resulting from the interaction between vision and cognition, and cognition properly speaking is the highest and entirely cognitive (Raftopoulos 2011, 6-9).

Before continuing with this explanation I would like to clarify the mean-ing of the concepts I will consider all along this thesis. In spite of the fact that, for Fodor, Pylyshyn and Raftopoulos, the visual system is defined as early vision, and cognition is understood as the conjunction of late vision and cognition properly speaking, hereafter, I prefer to refer to the earliest stage of cognition as ‘late vision’ and the latest (cognition properly speak-ing) simply as ‘cognition’. Furthermore, from now on I will consider the visual system as the conjunction of ‘early’ and ‘late’ vision, which are in-dependent from cognition (i.e., cognition properly speaking).²¹ Therefore, we can distinguish the visual system composed of an early and a late visual process (or subsystems). While early vision seems to process the incoming stimuli bottom-up or without external influences, late vision depends on the constant interaction between bottom-up incoming inputs and top-down (cognitive) information stored in memory.

The neuroanatomico-functional characterisation of late vision is in line with the one given for early vision. From a neuroanatomical point of view, early and late vision share common structures. Both are characterized as a visuo-motor system composed of a dorsal and a ventral streams as well as

20Late vision could be also considered as the process going from the retina to the perceptual experience, i.e., the conjunction of early vision and the subsequent visual processing. The reason for carving late vision as I do is to avoid confusion and determine a clear (if ever possible) boundary between both stages of visual processing.

21Whereas for Fodor, Pylyshyn and Raftopoulos the boundary between visual and cog-nitive systems is motivated by the beginning of cogcog-nitive influences on visual processing (i.e., after early vision), my distinction is based on the end of the perceptual processing (i.e., after late vision).

subcortical structures governing motor functions. From a functional per-spective, late vision involves larger and wider processing which recruits extra-visual structures.²² While early vision (Marr’s (1982) 3-D sketch and Hildreth’s and Ullman’s (1989) low- and intermediate-level vision) deliv-ers 3-D representations independently of cognitive influences, late vision (Hildreth’s and Ullman’s (1989) high-level vision) produces sophisticated outputs representing objects such as tables, cars, dogs, and the like.

To sum up, a neuroanatomico-functional characterization of late vision includes the dorsal and ventral streams as well as subcortical brain areas.

The difference with the early visual system lies on the spread of visual processing.

If perceptual experiences are the output of the visual system (understood as the conjunction of early and late vision), thus the visual processing seems to end when the perceptual experience is produced. That is, when the subject becomes conscious of this perceptual state. The time period of the late visual process is not easy to determine, the delivery of perceptual experiences depends on the kind of task, stimulus, environmental conditions, and many other features. I will provide a reasonable explanation of this time window (a similar account is given by Raftopoulos (2009a, ch. 2;2011). To do so, I will briefly discuss consciousness.

Any explanation of perceptual experiences requires an specific account of consciousness. The form of consciousness attributed to perceptual ex-periences which I will adopt here is spelled out by the Global Neuronal Workspace (GNW) theory by Dehaene et al. (1998, 2003); Dehaene and Changeux (2011); Dehaene and Naccache (2001). The GNW model pro-poses that consciousness (of perceptual, motor, or cognitive mental states) occurs when the (perceptual, motor, or cognitive) information is broadcast in a distributed neural network (a global neuronal workspace) which makes it accessible to the subject.

22Which other brain areas are exactly involved is an empirical matter beyond the scope of this thesis. The given definition is enough for my aims and it is of no harm for the argument that follows.

According to the GNW theory, conscious perceptual states could arise as early as 200 ms (the threshold of conscious experiences): when the percep-tual information becomes consciously accessible to the subject (Dehaene and Changeux 2011, 203-207, 215).²³ Even though only the information broadly broadcast in the workspace reach consciousness, all brain processes (con-sciously broadcast and unconscious) continue to contribute to the brain’s performance (Dehaene and Naccache 2001, 14). “A great many studies sug-gest that unconscious states play the same role in cognition, as do conscious states” (Pylyshyn 2003, 356). In addition, Lamme (2003, 16;2004, 869-871) remarks that subjects become conscious (access awareness) of their percep-tual experience in the time window between 200 and 300 ms (or sometimes more). Taking into consideration this empirical evidence, it could be argued that late vision is the process responsible for the deliverance of visual ex-periences, a process that lasts for about 100 to 200 ms after early vision. It begins at 100-120 ms post-stimulus onset and goes up to 200-300 ms, when the perceptual state becomes consciously accessible to the subject. (See also Melloni et al.(2011).)

There are three main reasons to interpret consciousness in terms of acces-sible mental states and explicate the phenomenon by appeal to the Global Neural Workspace (GNW) theory. Firstly, perceptual experiences are con-scious mental states the subject has access to. Philosophers of perception frequently discuss perceptual states as the sort of phenomenal state a sub-ject has when she sees an obsub-ject: what it looks like to have an experience.

Phenomenal states seem to be in some way reportable states, something subjects can refer to. This contrasts, e.g., with blindsighted subjects who do not seem to have perceptual experiences of one hemifield. Likewise, some epistemologists claim that perceptual beliefs are justified on the ba-sis of the perceptual experiences one has. For example, internalists such as

23Consciousness, from the GNW theory viewpoint, roughly coincides with access con-sciousness as defined by Block (1995, 1996, 2005), and also with Lamme’s (2000;2003;

2004) access awareness. Block(1995,1996,2005) gives a definition of two kinds of con-sciousness: phenomenal and access consciousness. A phenomenal and access awareness dichotomy is also defended by Lamme (2000, 2003, 2004) even though his distinction differs from the one given by Block.

accessibilists (Chisholm 1989;BonJour 2003) or internalist mentalists (Hue-mer 2001; Pryor 2000) and externalist mentalists (Alston 1993; Bergmann 2006;Burge 2003;Comesa˜na 2010; Dretske 2000; Engel 2007c, 2012a; Gra-ham 2011; Goldman 2008; Pollock and Cruz 1999).²⁴ Then, consciousness in epistemology and philosophy of perception involves some degree of ac-cess to the perceptual states. Secondly, the GNW theory provides a clear neural correlate of consciousness capable of explaining this access and de-grees of consciousness (consciousness does not seem to be an all or nothing phenomenon). The third reason is a practical one. The debate on cogni-tive penetration takes advantage of psychological studies in which subjects provide verbal reports or effectuate motor actions when they see an object (have a perceptual experience of it). Such verbal and motor responses imply the subject access to their own perceptual states. Therefore this character-isation of consciousness can be explained by the GNW theory (Dehaene et al. 1998;Dehaene and Naccache 2001;Dehaene et al. 2003;Dehaene and Changeux 2011), and seems to fit Block’s (1995; 1996; 2005) and Lamme’s (2000; 2003; 2004) concepts of access consciousness and access awareness respectively.

It is worthwhile observing that a clear distinction between time periods of visual processing depends on empirical evidence. Theories conflict with each other concerning the boundary between visual perception and cogni-tion. (And we could even cast doubt on the possibility of ever determining such a boundary, if it exists.) The time windows of early and late vision may change due to many factors (organism’s purposes, internal conditions, task performed, nature of the stimulus, time presentation, surrounding con-ditions, and the like). However, the uncertainty to find a clear boundary does not represent an issue for the idea that the visual process ends with the production of perceptual experiences. If we already accepted the distinction between early and late visual systems and the cognitive system, we have to

24This contrasts with the radical externalist view according to which perceptual ex-periences are not necessary for justification (Goldman 1979b, 1986; Lyons 2009, 2011;

Plantinga 1993).

admit that the late visual process must start at some point after the produc-tion of a primitive representaproduc-tion and end ultimately with the producproduc-tion of the perceptual experience. The relevant feature in this distinction is not whether the boundaries between vision and cognition are exact but whether it remains meaningful to distinguish these two processes.

To sum up, late vision appears to start at about 100 or 120 ms with the computation of the visual output delivered by early vision and ends when the system produces the perceptual experience. In normal subjects the late visual process could last between 100 and 200 ms (or even more) after early vision, the threshold of consciousness being approximately 200 ms post-stimulus onset (Dehaene and Changeux 2011, 203-207, 215;Lamme 2003, 16; 2004, 869-871; alsoMelloni et al. 2011). Once operations of recog-nition and categorization of the object are accomplished, the late visual system delivers a perceptual experience (the conscious mental state that subjects have while seeing an object). The subsequent stage to late vision is cognition.

There are two further reasons, in addition to the ones provided in section 2.1.1, to sustain my claim that perceptual experiences are the output of late (and not early) vision: the interaction between bottom-up and top-down processes and the time period of processing required to deliver an experience.

First of all, it has been pointed out that early vision seems to be imper-vious to cognitive influences; it only encodes bottom-up visual properties such as colour, shape, size, and the like. And without access to memory, the visual process cannot categorize or recognize the object (but see section2.3) (Fodor 1983, 64, 70-71; Pylyshyn 1999a, 361; 2003, 134-136). Recognition and categorization relies on the observer’s cognitive background, intentions, and point of view (Clark 2013, 187; Engel 1996, 282; Gilbert and Sigman 2007, 668; Pylyshyn 1984, 134-135; Raftopoulos 2001a, 427; 2005a, 75-76; 2009a, 77, 80). The late visual system makes possible the bottom-up and top-down interaction necessary to represent the object, i.e., to form a perceptual experience (Raftopoulos 2011, 6-9). This process cannot be

accomplished at the early visual stage.

Second, perceptual experiences are conscious mental states. It has been explained that consciousness arises, the earliest, at about 200 ms (Dehaene and Changeux 2011), a time period which is far from the end of early vision:

100-120 ms post-stimulus onset (Raftopoulos 2009a, ch. 2). If conscious-ness arises (or perceptual experiences are formed) in the time window of 200 to 300 ms after stimulus presentation the perceptual experience cannot be directly the output of early vision. The previous explanation coincides with Raftopoulos’ explanation and Stokes’ (ming, 36, fn. 20) observation thatRaftopoulos(2001c,2006) considers that “perceptual experience (later vision, if one likes) is affected in a top-down way” (my italics).

The possibility that the output of early vision could be consciously avail-able was not excluded. But it does not mean that the perceptual experience is produced immediately by early vision. Rather it might suggests that the content of the proto-object is preserved during the late visual process and eventually delivered in the perceptual experience. (I scrutinize this claim in section 2.3.)

To summarize, early vision is a very short period of bottom-up process-ing. Late vision, on the contrary, intimately depends on cognitive influences.

The bottom-up and top-down interaction happening during the late visual processing makes possible the recognition and categorization of primitive vi-sual objects. The result of this operation is the production of a perceptual experience.