Published online by Cambridge University Press: 30 January 2004
Neural correlates exist for a basic component of logical formulae, PREDICATE(x). Vision and audition research in primates and humans shows two independent neural pathways; one locates objects in body-centered space, the other attributes properties, such as colour, to objects. In vision these are the dorsal and ventral pathways. In audition, similarly separable “where” and “what” pathways exist. PREDICATE(x) is a schematic representation of the brain's integration of the two processes of delivery by the senses of the location of an arbitrary referent object, mapped in parietal cortex, and analysis of the properties of the referent by perceptual subsystems.
The brain computes actions using a few “deictic” variables pointing to objects. Parallels exist between such nonlinguistic variables and linguistic deictic devices. Indexicality and reference have linguistic and nonlinguistic (e.g., visual) versions, sharing the concept of attention. The individual variables of logical formulae are interpreted as corresponding to these mental variables. In computing action, the deictic variables are linked with “semantic” information about the objects, corresponding to logical predicates.
Mental scene descriptions are necessary for practical tasks of primates, and preexist language phylogenetically. The type of scene descriptions used by nonhuman primates would be reused for more complex cognitive, ultimately linguistic, purposes. The provision by the brain's sensory/perceptual systems of about four variables for temporary assignment to objects, and the separate processes of perceptual categorization of the objects so identified, constitute a pre-adaptive platform on which an early system for the linguistic description of scenes developed.
1. The logical formula is simplified for convenience here.
2. A complication to this picture arises from work on the recognitionof facial expressions by blindsight patients (de Gelder et al. 1999; 2000; Heywood & Kentridge 2000; Morris et al. 1999). Facial expressions are complex and are generally thought to require considerable higher-level analysis. Yet detection of facial expressions (e.g., sad, happy, fearful, angry) is possible in some blindsight patients, suggesting that some aspects of this task also are performed via a pathway that, like at least one dorsal pathway, bypasses primary visual cortex.
3. Belin and Zatorre (2000) suggest that the dorsal auditory pathway is involved in extracting the verbal message contained in a spoken sentence. This seems highly unlikely, as parsing a sentence appeals to higher-level lexical and grammatical information. The evidence they cite would only be relevant to the early pressure-sequence-to-spectrogram stages of spoken sentence processing.
4. Landau and Jackendoff (1993) is a more detailed version of Jackendoff and Landau (1992); I will refer here to the later paper, Landau and Jackendoff (1993).
5. Bertrand Russell at times espoused the view that particulars are in reality nothing but bundles of properties (Russell 1940; 1948; 1959). See also Armstrong (1978). There is also a phenomenalist view that “so-called material things, physical objects, are nothing but congeries of sensations” (Copi 1958).
6. Egly et al. (1994) state:
We found evidence for both space-based and object-based components to covert visual orienting in normal observers. Invalid cues produced a cost when attention had to be shifted from the cue to another location within the same object, demonstrating a space-based component to attention. However, the costs of invalid cues were significantly larger when attention had to be shifted an equivalent distance and direction to part of another object, demonstrating an object-based component as well. (p. 173)
This again conflates attention-shifting, a preattentive (and postattentive) process, with attention itself. These experiments relate only to attention-shifting, as the title of Egly et al.'s (1994) article implies. (Further, it would be interesting to know whether the distribution of RTs for the invalidly cued “within-object” attention shifts was in fact bimodal. If so, this could suggest that subjects were sometimes interpreting the end of a rectangle as a different object from the rectangle itself, and sometimes not. In this case, the responses taken to indicate a space-based process could in fact have been object-based.)
7. There is presumably a complex ecological balance between the information carried by a mental predicate and its frequency of use in the mental life of the creature concerned. Complex relations, if occurring frequently enough, might be somehow compressed into unitary mental predicates. An analogous case in language would be the common compressing of CAUSE(a, PRED(b) ) into a form with a single causative verb.
8. The claim in the text is not about memory limitations involved in parsing linguistic strings; it is about how many arguments the elementary propositions in the mind of a prelinguistic creature could have.
9. Both third and fourth person space in BSL are like available pronouns for entities being signed about, other than the speaker or hearer. It is not that BSL has four grammatical persons in the sense that English has three (1st – speaker, 2nd – hearer, 3rd – all other entities).
10. This formula, like any FOPL formula, conveys no temporal transitions. Tense logic is more complicated than FOPL.
11. See Batali (2002) for a computer simulation of the emergence of public language from representations of exactly this form.
12. Agre and Chapman (1987) do not, as stated by Ballard et al. (1995), use the term “deictic.”
13. Indeed, this quoted sentence contains the stem “refer-” four times, three times alluding to a visual process and once to a linguistic convention; probably few readers remark on the coincidence as in any way disturbing.
14. Notice in this quotation from Kant a faint forerunner of the idea developed in this article, that predicates are associated with processes more accessible to consciousness than arguments.