3 Block’s precision argument
What evidence speaks for Block’s thesis that “attended and foveal perception can be greater in [phenomenal precision] without involving awareness of more precise environmental properties” (this collection, p. 41)? (For those who have read the original article and have a firm grasp of the argument based on precision, this part may be skipped for the discussion in section 4.)
3.1 The stimulus and the conditions of viewing
Consider the stimuli in figure 1 taken from Carrasco et al. (2004, p. 310), and mentioned by Block twice (figure 7 and 9 in his article). It shows three Gabor patches of 16%, 22%, and 28% contrast—call these stimuli g16, g22, and g28 respectively. If we look directly (i.e., foveate) at and attend to each of these stimuli, the percepts they cause are decidedly different to each other. Call this condition “SFAG” for stimuli foveated, attention on gabors. However, if we fixate on the black spot between the patches (such that the patches are more in the periphery of our visual field) but attend to the one with lower contrast (i.e., to the left of where we fixate), then the percepts they cause appear indistinguishable from one another. Call this condition “SPAL” for stimuli peripheral, attention on lower contrast. This comparative indistinguishability does not arise if we attend to the higher contrast patch or to the spot in the middle. Call these conditions “SPAH” for stimuli peripheral, attention to higher contrast and “SPAF” for stimuli peripheral, attention to fixation spot, respectively.[7]
Table 1: The character in each condition of viewing/attending to the stimulus of 22% and 28% in figure 1. (See also footnote 7.)
Figure 1: If one fixates on one of the black dots but actively attends to the lower-contrast patch to the left, the two patches to the right and left of the dot will appear alike. If one gazes freely or attends to the right, the difference in contrast is obvious or even more pronounced. Taken from Carrascoet al. (2004, p. 310).
3.2 The evidence for attention influencing appearance
It seems that attention alters appearance. Our main evidence is introspective: we can reliably produce such changes in appearance from SPAH to SPAF to SPAL by shifting attention. This works even if we know of the effect.
To an external observer, there is evidence available from naïve subjects: If these subjects have to name the orientation of the patch with the higher contrast (↙ vs. ↘), they choose at chance level in SPAL even if there is a contrast difference of 6%.[8] (The shift in attention was exogenously triggered by a visual cue 27ms prior to stimulus onset.) Because subjects have to decide which grating looks higher in contrast, and pick the lower or the higher contrast patch at random, it is reasonable to assume that the two look the same: they have identical character in SPAL. Thus, attention affects appearance.
3.3 The contents and degree of r–precision in different conditions
So the character of comparative percepts (the character of experiencing two patches together) differs between these conditions, even if the stimuli and the way we fixate remain the same. But what about the respective contents?
In SFAG, we can clearly tell the patches apart. If percepts are constitutively veridical (because otherwise they are not percepts, but illusions or hallucinations), then the content of a percept is determined by the actual world. Thus, the content of each percept of a patch is (approximately) its actual contrast.[9]
In SPAF, the patches look different. However, as our ability to tell contrasts apart is a bit lower in the periphery, the contrast-JND is a bit higher—say, 3%.[10] So the content of the comparative percept is one where the content of each percept is less precise, but still discernible from another: its actual contrast within the range of a peripheral contrast-JND.
In SPAH, the comparative contrast between the patches is more pronounced. We cannot explain this if the content in SPAH is the same as in SPAF. Somehow, the contents ought to differ more than in SPAF. One way to do this is to see one as more r–precise than the other. Then it is easier to tell the two apart, because there is no content-overlap. Another way would be to assume that one becomes less r–precise. Then it is easier to tell them apart because the respective minima and maxima are further apart.[11]
In SPAL, the comparative percept (g22 & g28 together) is such that the two patches are indistinguishable. So our percept is strictly speaking non-veridical. In order to make it veridical, one has to assign a quite imprecise content: it must at least cover both actual contrasts—i.e., be greater or equal to the interval that includes the actual contrasts as endpoints: [22%, 28%].[12]
Table 2: The content and its degree of precision in each condition of viewing/attending to the stimulus of 22% and 28% in figure 1. (See also footnote 12.)
3.4 Estimating the degree of p–precision in the different conditions
So we know the percepts’ contents and r–precision in the different conditions—but how about their p–precision? Block agrees that this is hard to estimate correctly. But the PPP gives us a rough guide: if the percept of item i1 and the percept of item i2 are phenomenally indistinguishable with respect to some feature F under condition A, but phenomenally determinately different vis-à-vis F under condition B, then the experience in A is less precise than in B vis-à-vis F. However, the case becomes more complicated, because we also have to think of the p–precision of comparative percepts (experiences as a whole) in addition to the percepts compared (the parts of whole experiences), akin to what we did in the case of r–precision.
Perceptual wholes and perceptual parts
At each moment, you have a broad range of different sensations; but all of these together are parts of one massive phenomenal me-here-now-with-this-and-that-whole: at a bar, you smell the mixture of spilt beer and sweat, taste the medicinal-peaty taste of your Lagavulin, while you ogle a lovely co-member of your species—who makes you feel your heart pumping in your chest. But you don’t feel all these separately; they are fused into one fleeting holistic experience.
If phenomenal wholes are not character–identical, there must be a difference in their parts; but some distinguishable phenomenal wholes may still share parts with identical phenomenal character: the feel of your beating heart while ogling may be phenomenally identical to the feeling of your beating heart after escaping the oglee’s significant other.
3.4.2 Unattended parts can share character with attended parts
Just as temperature can alter the taste of sugar to caramel without being sugar or caramel, attention can affect phenomenal character without itself having a phenomenal character: attention alters the appearance of x, but there seems to be no additional phenomenal character as of attending to x. If so, then the phenomenal character of a perceptual part itself does not determine whether this part is attended to or not.[13] So a percept that is now in the attentional limelight may share its character with a counterpart in the attentional shadow: If I attend to a leaf in a tree, the leaf I focus on may look just as green as a leaf in my visual periphery that I experience but don’t care about. This is one interpretation of SPAL: the percept of the attended peripheral g22 shares its character with the percept of the unattended peripheral g28-patch.[14]
3.4.3 An estimation of –precision in the different conditionsp
Now, we may consider what the p–precision is in our cases. In SFAG, over the range of 1 foveal contrast-JND, all percepts look the same. This is the most p–precise that the character of a percept can be. The p–precision range is then roughly centered around some value n±x%, where x is approximately 1 foveally attended contrast-JND.[15]
In SPAF, the patches look determinately different; and in SPAH, they look even more different. It is in the spirit of PPP (see p. here) that the comparative percept in SPAH is more p–precise than the comparative percept in SPAF.
But because the character of a percept is independent of whether one attends to or foveates on it, each compared percept (the parts of which the comparative percept is composed) ought to be similarly p–precise as in SFAG: if parts inside and outside the focus of attention can share phenomenal character, and if this holds for all characters, then the same range of characters can appear anywhere in our visual experience. So we ought to expect the same range of PPP–cases in the periphery as in the fovea. Then, the character ought to count as similarly p–precise.
3.5 The argument
If I am correct so far, we can state the following: (P1) If the character of an attended and an unattended percept can be identical (section 3.4.2), then perceptual parts are overall more p–precise than r–precise, because the range of p–precision–values of compared percepts is stable in all conditions (table 3), but the range of r–precision must vary in order to account for the veridicality of percepts (table 2). (P2) If the character of an attended and an unattended percept can be identical, then our compared percepts (the parts of the comparative percept) are more p–precise than r–precise in SPAL.[16] But if GR were true, then there must be a representational feature that accounts for each phenomenal feature. This applies to precision as well, because—according to Block—p–precision is a phenomenal feature of one’s perception. So if GR were true, representational precision must account for phenomenal precision. But (P1) and (P2) stand in direct opposition to this. So, by modus tollens, GR ought to be considered false.
Table 3: The approximated phenomenal precision in each condition of viewing/attending. How p–precise the comparative percepts (g22&g28 perceived together) are can be ordered from lowest to highest: SPAH>SPAF>SPAL. (See also footnotes 7 and 12.)
