Multistability in perception: binding sensory modalities, an overview

This special issue presents research concerning multistable perception in different sensory modalities. Multistability occurs when a single physical stimulus produces alternations between different subjective percepts. Multistability was first described for vision, where it occurs, for example, when different stimuli are presented to the two eyes or for certain ambiguous figures. It has since been described for other sensory modalities, including audition, touch and olfaction. The key features of multistability are: (i) stimuli have more than one plausible perceptual organization; (ii) these organizations are not compatible with each other. We argue here that most if not all cases of multistability are based on competition in selecting and binding stimulus information. Binding refers to the process whereby the different attributes of objects in the environment, as represented in the sensory array, are bound together within our perceptual systems, to provide a coherent interpretation of the world around us. We argue that multistability can be used as a method for studying binding processes within and across sensory modalities. We emphasize this theme while presenting an outline of the papers in this issue. We end with some thoughts about open directions and avenues for further research.     

Ashéninka amity: a study of social relations in an Amazonian society

Starting with Ashéninka people's avowed preference for living apart, in nuclear family households, this article analyses Ashéninka social practices within the context of ongoing academic debates over reciprocity, kinship, and the relative importance of similarity and difference in Amazonian thought. I argue that instead of attempting to pull others into fixed and narrowly prescribed relationships, particularly those based on kinship, the Ashéninka prefer for all ties to be based on relations of friendship that remain voluntary, limited, and flexible. I show how these relationships are underpinned by a cultural imperative on unilateral giving that is manifested in masateadas , social gatherings centred on the consumption of manioc beer.  

Résumé

À partir de la préférence déclarée des Ashéninkas pour une vie isolée en maisonnées composées de familles nucléaires, l'article analyse les pratiques sociales dans le contexte des débats académiques actuels sur la réciprocité, la parenté et l'importance relative de la similitude et de la différence dans la pensée amazonienne. L'auteur avance qu'au lieu de tenter de contraindre les autres à des relations fixes et strictement prescrites, notamment sur la base de la parenté, les Ashéninkas préfèrent qu'elles soient tissées à partir de liens d'amitié volontaires, limités et souples. L'auteur montre comment ces relations sont sous-tendues par un impératif culturel de don unilatéral, manifesté dans les masateadas , des rassemblements sociaux centrés sur la consommation de bière de manioc.     

On the accuracy of perceived parental height in a native Amazonian society

Studies of secular trends in adult height in rural pre-literate societies are likely to show no change owing to random measurement error in age. In such societies, adults lack birth certificates and guess when estimating their age. We assess the accuracy of perceived height of the same-sex parent to estimate secular trends. We tested the method among the Tsimane', a native Amazonian society of farmers and foragers in Bolivia. Subjects included 268 women and 287 men >20 years of age. Over half the sample reported inaccurately the height of their same-sex living parent, with a tendency to report no difference when, in fact, differences existed. Results highlight the pitfalls of using perceived parental height to examine secular trends in adult height among the Tsimane', though the method might yield accurate information in other societies. We discuss possible reasons for the low accuracy of Tsimane' estimates.     

Face to face: meaning, feeling and perception in Amazonian welcoming ceremonies

Some welcoming ceremonies practised by indigenous peoples of the Amazon have been considered events that enable the establishment of a social link between potential enemies. The studies do not, however, indicate how the shift from latent hostility to a social relationship occurs. They only refer to the 'magical act' produced through the significant exchange during the dialogues that take place at the key moment of the ceremony. Examining the perceptual interaction of the Candoshi welcoming ceremony and not merely the text of the dialogue, this article attempts to incorporate into the analysis the intensity of the affective dimension which governs these rituals, which can help to explain how such rituals provide the participants with the confidence to initiate a social relationship.     

Natural selection in the water: freshwater invasion and adaptation by water colour in the Amazonian pufferfish

Natural selection and ecological adaptation are ultimately responsible for much of the origin of biodiversity. Yet, the identification of divergent natural selection has been hindered by the spatial complexity of natural systems, the difficulty in identifying genes under selection and their relationship to environment, and the confounding genomic effects of time. Here, we employed genome scans, population genetics and sequence-based phylogeographic methods to identify divergent natural selection on population boundaries in a freshwater invader, the Amazonian pufferfish, Colomesus asellus. We sampled extensively across markedly different hydrochemical settings in the Amazon Basin and use 'water colour' to test for ecological isolation. We distinguish the relative contribution of natural selection across hydrochemical gradients from biogeographic history in the origin and maintenance of population boundaries within a single species and across a complex ecosystem. We show that spatially distinct population structure generated by multiple forces (i.e. water colour and vicariant biogeographic history) can be identified if the confounding effects of genetic drift have not accumulated between selective populations. Our findings have repercussions for studies aimed at identifying engines of biodiversity and assessing their temporal progression in understudied and ecologically complex tropical ecosystems.     

Visual development: experience puts the colour in life

Recent findings show that colour processing, like most other sensory attributes, is shaped by experience. While such studies can reveal the mechanisms of development, can they also help uncover the mechanisms of perception?     

Statin use and peripheral sensory perception: A pilot study

Objectives. Peripheral sensory neuropathy is a neurological deficit resulting in decreased detection of sensation through the peripheral nervous system. Peripheral sensory neuropathy is commonly diagnosed with the use of a monofilament and either a tuning fork or neurothesiometer. Statins are a widely used medication and there has been some debate of association with their use and peripheral sensory neuropathy. This pilot study aimed to test the sensory perception of participants with long-term statin use and compare these results to their peers who were not taking statins.

Methods. Thirty participants were recruited and equally divided into a statin and non-statin group. Healthy participants were screened by their medical and medication history, Australian Type 2 Diabetes Risk assessment, and random blood glucose level. An assessor who was blinded to the participant group conducted sensory assessments using a 10?g monofilament and neurothesiometer.

Results. There was no difference in monofilament testing results between the groups. The statin group was less sensate at the styloid process (p?=?0.031) and medial malleolus (p?=?0.003) than the control group. Results at the hallux were not statistically significant (p?=?0.183).

Conclusion. This result is suggestive of a potential association between long-term statin use and a decrease in peripheral sensory perception. This may be because of peripheral sensory neuropathy. Limitations such as consideration of participant height, participant numbers, and inability to analyze results against statin groups are reported. As statins are a life-saving medication, careful consideration should be applied to these results and further research be conducted to determine if these results are applicable to larger populations.     

The interaction of innate and imposed colour perception: a behavioural approach

Nile tilapia were raised from eggs to 2 months of age under a coloured light regime (violet, blue, green, yellow, and red) and then tested for colour preference in a multiple chamber maze with different colour options. Fish were observed individually during three days at 8, 11, 14, and 17 h, every 2 min for 20 min and the visit frequency in each compartment was analyzed. Young Nile tilapia kept under yellow and red light showed preference for yellow and red, respectively. Fish held under violet, blue, and green light did not show any colour preference or avoidance. These results imply that environmental colour affects colour preference of Nile tilapia, possibly due to light-dependent shift of visual pigments in the retina, indicating that colour preference is not an innate response. This conclusion reinforces the idea that environmental colour modulates fish physiological and behavioural processes.     

Assortative mating and offspring well-being: theory and empirical findings from a native Amazonian society in Bolivia

Mate choice matters for inclusive fitness, household economic efficiency, assimilation, stratification, and economic inequalities in society. In positive assortative mating, people pair with someone who resembles them along a trait, whereas in negative assortative mating, people pair with someone who differs from them along a trait. In industrial nations, people tend to follow positive assortative mating for fundamental demographic dimensions (e.g., age, schooling) and might practice negative assortative mating for economic outcomes (e.g., earnings). Research on assortative mating has focused on industrial nations, generally compared only one trait between couples, and paid scant attention to the effects of assortative mating for offspring well-being. If assortative mating enhances inclusive fitness, it might also enhance offspring well-being. Drawing on data from a farming–foraging society in the Bolivian Amazon (Tsimane') that practices preferential cross-cousin marriage, we (a) identify six parental traits (age, knowledge, wealth, schooling, height, and smiles) for which Tsimane' might practice assortative mating and (b) test the hypothesis that assortative mating enhances offspring well-being. Proxies for offspring well-being include height and school attainment. Tsimane' resemble people of industrial nations in practicing mostly positive assortative mating. Pairwise, mother–father and Pearson correlations of age, schooling, and earnings among Tsimane' resemble correlations of industrial nations. Correlation coefficients for the six parental traits were far higher than correlations that might happened just by chance. We found weak support for the hypothesis that assortative mating improves offspring well-being.     

Consuming Grief: Compassionate Cannibalism in an Amazonian Society

Consuming Grief: Compassionate Cannibalism in an Amazonian Society. Beth A. Conklin. Austin: University of Texas Press, 2001. 317 pp.     

Design and perception: Making the zoo experience real

The purpose of this paper is to encourage the application of theories of human behavior to zoo design so that zoo visitors are environmentally predisposed to learn from and enjoy what they experience. The ultimate goal is to increase public awareness and appreciation of the importance of habitat and its protection to wildlife conservation and to present zoo animals in such a way that their reason for being and rights to existence are intuitively self-evident to viewers. Many of the concepts and guidelines presented appear to be suitable subjects of behavioral research, whose findings would assist designers and other zoo professionals in continued improvement of the zoo visitor's experience.     

Comparing sensory experience in bitter taste perception of phenylthiocarbamide within and between human twins and singletons: intrapair differences in thresholds and genetic variance estimates

BACKGROUND: Quantitative genetic studies revealed that not all of the phenotypic variance in PTC taste perception is heritable. AIM: To study quantitative variations in PTC tasting ability in twins and to estimate heritability of PTC taste perception on the taste of twin data on males and females sexes separately. SUBJECTS AND METHODS: The data for PTC taste sensitivity following the classic method of Harris & Kalmus (1949) were collected on a sample of 141 twin pairs (66 MZ and 75 DZ) and 275 singletons (128 males and 147 females) from Chandigarh, India. Genetic analyses were performed following Christian (1979), Donner (1986) and Sham (1998). RESULTS: Frequency of non-tasters was similar in twins (33 %) and singletons (32 %), but significant sex differences were observed. No differences were found between zygosities for mean thresholds. Similarly, no evidence of variance heterogeneity and environmental covariance was seen between zygosities. Since no basic assumption of the twin method was found violated, within-pair estimates of genetic variance would be unbiased. These estimates were highly significant in both males and females. However, dominance and additive components of genetic variance were found to differ between sexes. CONCLUSION: PTC thresholds do not seem to be significantly affected by environmental factors as no variance inequality was observed between twin zygosities. Intensity of bitterness (scalar dimensions) of PTC is a separate trait having no commonality with the genetic basis of recognition threshold for PTC tasting ability. The receptors recognizing bitter taste are different from the receptors determining intensity of taste. The absolute difference between co-twins in PTC thresholds can be used as a simple tool in the twin zygosity diagnosis. The results show that none of the MZ co-twins had manifested difference of more than 3 in their PTC threshold.     

Amazonian peatlands: an ignored C sink and potential source

In tropical lowlands, peatlands are commonly reported from Southeast Asia, and especially Indonesian tropical peatlands are known as considerable C sinks and sources. In contrast, Amazonia has been clearly understudied in this context. In this study, based on field observations from 17 wetland sites in Peruvian lowland Amazonia, we report 0–5.9 m thick peat deposits from 16 sites. Only one of the studied sites did not contain any kind of peat deposit (considering pure peat and clayey peat). Historic yearly peat and C accumulation rates, based on radiocarbon dating of peat samples from five sites, varied from 0.94 ± 0.99 to 4.88 ± 1.65 mm, and from 26 ± 3 to 195 ± 70 g C m⁻², respectively. The long-term apparent peat and C accumulation rates varied from 1.69 ± 0.03 to 2.56 ± 0.12 mm yr⁻¹, and from 39 ± 10 to 85 ± 30 g C m⁻² yr⁻¹, respectively. These accumulation rates are comparable to those determined in the Indonesian tropical peatlands. Under altered conditions, Indonesian peatlands can release globally relevant amounts of C to the atmosphere. Considering the estimated total area of Amazonian peatlands (150 000 km²) close to that of the Indonesian ones (200 728 km²) as well as several factors threatening the Amazonian peatlands, we suggest that the total C stocks and fluxes associated with Amazonian peatlands may be of global significance.     

Child undernutrition in war-torn society: the Ethiopian experience.

Using data from a cross-sectional nutrition survey conducted in rural Ethiopia between March and April 1992, roughly a year after the end of one of the longest civil wars in modern human history, this study attempts to document the magnitude and correlates of childhood undernutrition in Ethiopia. Findings from the study reveal that, at the time of the survey, 59% of children in the country were exposed to long-term or chronic undernutrition (stunted); about 4% were suffering from acute problems (wasted); and about the same proportion were both stunted and wasted. Less than a third of the country's children had normal growth. The logistic-binomial regression results demonstrated the existence of significant clustering of risks of undernutrition within areas of residence and notable differentials by age of child, duration of breast-feeding, age at introduction of supplementary foods and number of under-five siblings. Significant variations were also noted by age of household head, per capita land holding, religious affiliation and prevalence of endemic diseases in an area.     

Fire-mediated dieback and compositional cascade in an Amazonian forest

The only fully coupled land-atmosphere global climate model predicts a widespread dieback of Amazonian forest cover through reduced precipitation. Although these predictions are controversial, the structural and compositional resilience of Amazonian forests may also have been overestimated, as current vegetation models fail to consider the potential role of fire in the degradation of forest ecosystems. We examine forest structure and composition in the Arapiuns River basin in the central Brazilian Amazon, evaluating post-fire forest recovery and the consequences of recurrent fires for the patterns of dominance of tree species. We surveyed tree plots in unburned and once-burned forests examined 1, 3 and 9 years after an unprecedented fire event, in twice-burned forests examined 3 and 9 years after fire and in thrice-burned forests examined 5 years after the most recent fire event. The number of trees recorded in unburned primary forest control plots was stable over time. However, in both once- and twice-burned forest plots, there was a marked recruitment into the 10-20cm diameter at breast height tree size classes between 3 and 9 years post-fire. Considering tree assemblage composition 9 years after the first fire contact, we observed (i) a clear pattern of community turnover among small trees and the most abundant shrubs and saplings, and (ii) that species that were common in any of the four burn treatments (unburned, once-, twice- and thrice-burned) were often rare or entirely absent in other burn treatments. We conclude that episodic wildfires can lead to drastic changes in forest structure and composition, with cascading shifts in forest composition following each additional fire event. Finally, we use these results to evaluate the validity of the savannization paradigm.