Corso di Laurea Specialistica in Sistemi e Progetti di Comunicazione
Anno Accademico 2005 – 2006
Linguaggio e Comunicazione (LO042)
Alessandro Lenci
Dipartimento di linguistica “T. Bolelli”
via Santa Maria 36 – 56100 PISA
31 ottobre 2006
__________
1. Codice e inferenza
“Inference is cheap, articulation expensive, and thus the articulation design are for a system that
maximizes inference. […] Linguistic content has to be thought of less like definitive content and
more like interpretive clue” (Levinson 2000: 28).
“We define grammar as the class of possible solutions to the problem of mapping back and forth
between a high-dimensional meaning space with universal properties and a low-dimensional
channel that unfolds in time, heavily constrained by limits of information processing. […] This
is a constrained satisfaction problem and also a dimension reduction problem. In problems like
this complex solutions are likely to emerge that are not directly predictable from any individual
component” (Bates e Goodman 1999, “On the emergence of grammar from the lexicon. In B.
MacWhinney (Ed.), The emergence of language (pp. 29-80). Mahwah, NJ: Lawrence Erlbaum
Associates)
2. La comunicazione come coordinamento tacito
“Whatever the correct explanation of the meeting of the minds in successful communication, the
basic insight underlying Grice’s account of speaker meaning is that communication is like a game
of tacit coordination: the speaker intends the hearer to reason in a certain way partly on the basis
of being so intended. That is, the hearer is to take into account that he is intended to figure out the
speaker’s communicative intention. It is the meaning of the words uttered, of course, that provides
the input to this inference, but what they mean does not determine what the speaker means” (Bach
1994, “Meaning, Speech Acts and Communication”, in Basic Topics in the Philosophy of
Language, Robert M. Harnish (ed.), Prentice-Hall 1994)
Giochi di coordinamento: interazioni in cui ciascun agente riceve un guadagno dallo scegliere la
stessa mossa di un altro agente
Schelling (1960), The Strategy of Conflict
Gli agenti tendono a coordinare le loro azioni scegliendo le opzioni più salienti per entrambi:
“providing everyone with some clue for coordinating behavior, some focal point for each person’s
expectation of what the other expects him to expect to be expected to do” (p. 57).
2. La comunicazione linguistica come “constrained informational enrichment”
Due requisiti fondamentali della comunicazione linguistica:
1. “use inferential enrichment to bypass this physiological limitation” (cf. il collo di bottiglia
articolatorio);
2. “the inferential enrichment must be circumscribed in such a way that communicators can indeed
zero-in or coordinate (in the Schelling sense) on the correct communicative forms and heuristics”
“What our pirots clearly need is a set of heuristics, mutually assumed by sender and receiver, that
can serve to multiply the coded information by a factor of, say, three, by licensing inferential
enrichment of what is actually encoded by a choice of a specific signal. These heuristics must at the
same time constrain that enrichment, in such a way that the overall message can still be correctly
recovered, by guiding (or coordinating) the match between the chosen signal and the recoverable,
augmented message” (Levinson 2000: 31)
3. Cosa è l’informazione
Alcune proprietà fondamentali dell’informazione:
- può essere codificata;
- può essere trasmessa;
- può essere de-codificata e memorizzata;
- è additiva;
- è non negativa;
Teoria matematica dell’informazione - Shannon 1948
Approccio quantitativo all’informazione che cerca di rispondere alla domanda: quanto piccolo può
essere un messaggio, a parità di contenuto di informazione che deve essere trasmesso? (problema
di compressione)
Quantità di informazione
Dato un alfabeto di N simboli equiprobabili, la quantità di informazione per simbolo (incertezza) è
log2N (bits)
Sistema
luce fissa
interruttore binario, moneta, ecc.
semaforo
due monete
3 monete
Alfabeto
1 simbolo
2 simboli
3 simboli
4 simboli
8 simboli
Bits di informazione per simbolo
log(1) = 0
log(2) = 1
log(3) = 1,58
log(4) = 2
log(8) = 3
Teoria logico-filosofica dell’informazione – Bar-Hillel & Carnap 1952, Dretske 1981, et al.
“Inverse Relationship Principle refers to the inverse relation between the probability of p —
which may range over sentences of a given language (as in Bar-Hillel and Carnap) or events,
situations or possible worlds (as in Dretske) — and the amount of semantic information
carried by p … It states that information goes hand in hand with unpredictability. Popper
[1935] is often credited as the first philosopher to have advocated IRP explicitly. However,
systematic attempts to develop a formal calculus involving it were made only after Shannon's
breakthrough.”
Valore informativo (quantità di informazione) di messaggio – il numero di stati di un sistema che il
messaggio è in grado di esclude (dato un certo dominio)
4. Euristiche per l’arricchimento inferenziale
“To increase the informativeness of a coded message which itself rules out some number n of states
of affairs, and thus to overcome the limit on the rate of encoding, all we need are some heuristics
that will serve to rule out some further possible states, yielding an incremented content n+m.”
(Levinson 2000: 31)
Tre euristiche per l’incremento dell’informatività (prima formulazione informale)
Euristica 1 - “Ciò che non è stato detto, non vale”
Euristica 2 – “Ciò che è stato detto in maniera normale, vale in modo normale”
Euristica 3 – “Ciò che è stato detto in maniera inusuale, vale in maniera inusuale”
“Each heuristic allows the recipient of a message to rule out a great many states of affairs that are
in fact compatible with the content of coded message. Taken together, the set of a three heuristics
serves to multiply the informational content of any message by a factor of perhaps a score,
transforming the slow coding rate of human speech into smoothing approximating the perceived
speed of human communication. All that is required for such a system to work is a tacit agreement
between communicators that such heuristics can be assumed to be operative […]. At the same
time, because the heuristics effectively narrow the range of intended extensions of a expressions,
they will significantly constrain the search space for speakers’ intention and thus help to resolve
the logical problem of intention recovery” (Levinson 2000: 34).