Miller (1956) summarized evidence that people can remember about seven chunks in short-term memory (STM) tasks. How- ever, that number was meant more as a rough estimate and a rhetorical device than as a real capacity limit. Others have since suggested that there is a more precise capacity limit, but that it is only three to five chunks. The present target article brings together a wide vari- ety of data on capacity limits suggesting that the smaller capacity limit is real. Capacity limits will be useful in analyses of information processing only if the boundary conditions for observing them can be carefully described. Four basic conditions in which chunks can be identified and capacity limits can accordingly be observed are: (1) when information overload limits chunks to individual stimulus items, (2) when other steps are taken specifically to block the recoding of stimulus items into larger chunks, (3) in performance discontinuities caused by the capacity limit, and (4) in various indirect effects of the capacity limit. Under these conditions, rehearsal and long-term memory cannot be used to combine stimulus items into chunks of an unknown size; nor can storage mechanisms that are not capacity- limited, such as sensory memory, allow the capacity-limited storage mechanism to be refilled during recall. A single, central capacity limit averaging about four chunks is implicated along with other, noncapacity-limited sources. The pure STM capacity limit expressed in chunks is distinguished from compound STM limits obtained when the number of separately held chunks is unclear. Reasons why pure capacity estimates fall within a narrow range are discussed and a capacity limit for the focus of attention is proposed.

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The magical number 4 in short-term memory: a reconsideration of mental storage capacity.

We argue that an understanding of the faculty of language requires substantial interdisciplinary cooperation. We suggest how current developments in linguistics can be profitably wedded to work in evolutionary biology, anthropology, psychology, and neuroscience. We submit that a distinction should be made between the faculty of language in the broad sense (FLB)and in the narrow sense (FLN) . FLB includes a sensory-motor system, a conceptual-intentional system, and the computational mechanisms for recursion, providing the capacity to generate an infinite range of expressions from a finite set of elements. We hypothesize that FLN only includes recursion and is the only uniquely human component of the faculty of language. We further argue that FLN may have evolved for reasons other than language, hence comparative studies might look for evidence of such computations outside of the domain of communication (for example, number, navigation, and social relations).

/pdf/the-faculty-of-language-what-is-it-who-has-it-and-how-did-it-2ls6go98wi.pdf

The faculty of language: what is it, who has it, and how did it evolve?

A DNA test to sex most birds.

General Themes: G.A. Parker, Sperm Competition and the Evolution of Ejaculates: Towards a Theory Base. A.P. Moller, Sperm Competition and Sexual Selection. W.G. Eberhard, Female Roles in Sperm Competition. J. Wright, Paternity and Paternal Care. Taxonomic Treatments: L.F. Delph and K. Havens, Pollen Competition in Flowering Plants. D.R. Levitan, Sperm Limitation, Gamete Competition and Sexual Selection in External Fertilizers. N.K. Michiels, Mating Conflicts and Sperm Competition in Simultaneous Hermaphrodites. B. Baur, Sperm Competition in Molluscs. M.A. Elgar, Sperm Competition and Sexual Selection in Spiders and Other Arachnids. L.W. Simmons and M.T. Siva-Jothy, Sperm Competition in Insects: Mechanisms and the Potential for Selection. C.W. Petersen and R.R. Warner, Sperm Competition in Fishes. T.R. Halliday, Sperm Competition in Amphibians. M. Olsson and T. Madsen, Sexual Selection and Sperm Competition in Reptiles. T.R. Birkhead, Sperm Competition in Birds: Mechanisms and Function. D.A. Taggart, W.G. Breed, P.D. Temple-Smith, A. Purvis, and G. Shimmin, Reproduction, Mating Strategies and Sperm Competition in Marsupials and Monotremes. M. Gomendio, A.H. Harcourt, and E.R.S. Roldan, Sperm Competition in Mammals. T.R. Birkhead and A.P. Moller, Sperm Competition, Sexual Selection and Different Routes to Fitness. Index.

Sperm competition and sexual selection

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation1,2,3,4,5,6,7. Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumulated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans8,9,10,11. We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds12,13. The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinctive, a phenomenon characteristic of human cultures14 but previously unrecognised in non-human species.

Cultures in chimpanzees

Songbirds learn the songs that they sing from other individuals, but the learning is not always accurate. This leads to dialects and to changes with time in the songs found in one place. Are these phenomena functional or are they simply byproducts of vocal learning which has evolved for quite different reasons?

The cultural transmission of bird song.

The temporal pattern of feeding in the zebra finch

Fifty years of bird song research: a case study in animal behaviour

Song characteristics are age dependent in the willow warbler, Phylloscopus trochilus

In a population of chaffinches (Fringilla coelebs) some song types are produced by many individuals while others occur only in the repertoire of single individuals. This frequency distribution of song types fits that predicted from a model for the frequency of neutral alleles, suggesting that song types are copied at random rather than some being favoured over others. Both comparison with this model and computer simulations suggest that the "mutation rate" in song copying is around 15%, changes in this case arising either through immigration or because of inaccuracies in copying. Such a rate of change would also lead the songs present to change with time to much the same extent as we have found. No evidence could be found that particular combinations of song types tended to occur more often than expected in the same repertoire, suggesting that repertoires are built up by copying from more than one individual. Rare songs (those unique to a particular individual in the population) do, however, tend to cluster in the same repertoire, probably because some of the birds possessing them are immigrants. Repertoire size clusters at around 2-3 song types but is not significantly different from that predicted if birds can learn the same song type more than once so that their observed repertoire size is smaller than that which they actually possess.

Peter J. B. Slater

Papers

The cultural transmission of bird song.

The temporal pattern of feeding in the zebra finch

Fifty years of bird song research: a case study in animal behaviour

Song characteristics are age dependent in the willow warbler, Phylloscopus trochilus

Chaffinch Song Types: Their Frequencies in the Population and Distribution Between Repertoires of Different Individuals