Words can be matched with the concept of sign (correspondence of a signifier to a signified) as long as they act as symbol-words endowed with some semantic self-sufficiency. But in discourse, they lose their wholeness as symbol-words and metamorphose into wording-symbols. They, suddenly, appear as mere signifier entities with a more or less loose allusion to their status as cultural symbols. In discourse, words are no longer signs but tools covering ephemeral collections of neurosemes: the link of the sign breaks as soon as discourse takes over. The referential potential is no longer the schematic meaning issued from culture, but the universe of discourse under construction. This is why any attempt to account for meaning in language must integrate the neural process of meaning creation. It is now established that meaning is not the result of language activity but the result of cognition. However, what language does, via discourse, is to make this meaning communicable. For all these reasons, the task of linguistics should be to investigate the relationship between cognition and linguistic output in order to shed light on all the cognitive traces left within the surface strings. The role of morphosyntax thus has to be re-evaluated in this light.

A mathematical model is presented that obeys a strong form of Weber's law – over a range of adapting and stimulus intensities, equal contrast stimuli evoke identical responses. To account for the strong Weber's law, the adaptive stage in the proposed model employs a “delayed” reverse reaction along with a power-law input. It is suggested that this Weber's law mechanism is responsible for a slow, voltage-uncorrelated component of adaptation in the vertebrate photoreceptor. A plausible biochemical mechanism is the G-protein cycle with phosphorylation of photoactivated photopigment (and binding of arrestin to the phosphorylated photopigment) as the adaptive process. In an Appendix, features of the general model and implications of a specific biochemical model are examined by computer simulation.

Light causes a rapid, 1.7-fold increase in cyclic GMP concentration in intact squid retinas (Johnson et al. (1986)). To determine whether light-induced changes in cyclic GMP concentration result from activation of guanylate cyclase, we have studied the regulation of guanylate cyclase activity in squid (Loligo pealei) photoreceptors. The enzyme is membrane-associated and activity is enhanced by the detergents Triton X-100 or digitonin. The enzyme requires divalent cations, Mn2+ being preferred over Mg2+. The dependence of enzyme activity on the MnGTP concentration deviates from simple Michaelis-Menten kinetics. Under conditions where a light-induced binding of GTP to the guanine nucleotide regulatory protein can be observed, no light-induced change in guanylate cyclase could be detected.