Optimality of collective choices: a stochastic approach.

Amplifying communication is a characteristic of group-living animals. This study is concerned with food recruitment by chemical means, known to be associated with foraging in most ant colonies but also with defence or nest moving. A stochastic approach of collective choices made by ants faced with different sources is developed to account for the fluctuations inherent to the recruitment process. It has been established that ants are able to optimize their foraging by selecting the most rewarding source. Our results not only confirm that selection is the result of a trail modulation according to food quality but also show the existence of an optimal quantity of laid pheromone for which the selection of a source is at the maximum, whatever the difference between the two sources might be. In terms of colony size, large colonies more easily focus their activity on one source. Moreover, the selection of the rich source is more efficient if many individuals lay small quantities of pheromone, instead of a small group of individuals laying a higher trail amount. These properties due to the stochasticity of the recruitment process can be extended to other social phenomena in which competition between different sources of information occurs.

Mismatch negativity evoked by the McGurk-MacDonald effect: a phonetic representation within short-term memory.

OBJECTIVES: The McGurk-MacDonald illusory percept is obtained by dubbing an incongruent articulatory movement on an auditory phoneme. This type of audiovisual speech perception contributes to the assessment of theories of speech perception. The mismatch negativity (MMN) reflects the detection of a deviant stimulus within the auditory short-term memory and besides an acoustic component, possesses, under certain conditions, a phonetic one. The present study assessed the existence of an MMN evoked by McGurk-MacDonald percepts elicited by audiovisual stimuli with constant auditory components. METHODS: Cortical evoked potentials were recorded using the oddball paradigm on 8 adults in 3 experimental conditions: auditory alone, visual alone and audiovisual stimulation. Obtaining illusory percepts was confirmed in an additional psychophysical condition. RESULTS: The auditory deviant syllables and the audiovisual incongruent syllables elicited a significant MMN at Fz. In the visual condition, no negativity was observed either at Fz, or at O(z). CONCLUSIONS: An MMN can be evoked by visual articulatory deviants, provided they are presented in a suitable auditory context leading to a phonetically significant interaction. The recording of an MMN elicited by illusory McGurk percepts suggests that audiovisual integration mechanisms in speech take place rather early during the perceptual processes.

Estimated subglottic pressure in normal and dysphonic subjects.

The objective of this report was to study the clinical interest of estimated subglottic pressure (ESGP) with measurements of intraoral pressure according to the "airway interrupted method." Twenty healthy female subjects and 27 dysphonic female patients were included and asked to produce sounds under different conditions of pitch and intensity. The ESGP increased with intensity and slightly with pitch in both patients and controls. A comparison between patients and controls showed significantly higher values of ESGP in patients under all conditions of intensity and pitch. For normal intensity and usual pitch, ESGP has been found to be 6.1 hectopascals (hPa) in control subjects and 8.25 hPa in patients (p = .002). Discriminant analysis of all the measured data showed that data recorded for low intensity (lowest possible intensity without whispering) and high pitch (9 semitones above the usual pitch) were the most discriminant. The authors concluded that ESGP allows good discrimination between dysphonic patients and control subjects and might be included in the basic clinical set of objective parameters.