The contribution of specific contextual attributes to recognition of a well-learned cue was examined in four experiments with 6-month-olds. 24 h after learning to move a given mobile in a distinctive visual surround by kicking, recognition of the training cue was tested in either the original context or in one in which only a single contextual attribute was altered. Retrieval was completely disrupted by all form changes involving the deletion of angles and by a chromatic figure/ground reversal, but a discriminable change in form color had no effect. Although infants displayed partial retention in a degraded context after 1 day, they displayed no retention when a reminder was administered in the same degraded context after 20 days. These data reveal that infants do not encode contextual information holistically; moreover, they imply a privileged status for highly specific information about the incidental setting in which an event occurs. Unless this same highly specific information is perceptually identified at the time of testing, the memory of that event will not be retrieved. These data are consistent with our hypothesis that the visual context serves as an initial attention gate for memory retrieval.A common finding in studies of animals, children, and adults is that retention is better the greater the similarity between the encoding and retrieval contexts (

The ability of 6-month-old infants to remember a functional category acquired in a specific context was assessed in 3 experiments via an operant procedure in which infants learned to perform a specific action (a footkick) to activate an object suspended before them. In Experiment 1, infants trained with different exemplars in the same context transferred responding to a novel exemplar in the same but not a different context 24 hours later. Experiment 2 revealed that infants' reactivated memory of category training remained intact and context-specific after 3 weeks. In Experiment 3, a novel category exemplar was able to reactivate the forgotten memory of category training only in the encoding context. At 6 months, information about the place where categories are constructed is prerequisite for retrieval of a category concept from long-term memory. This requirement insures that early category concepts remain stable over relatively long periods.

The ability of 6-month-old infants to remember a functional category acquired in a specific context was assessed in 3 experiments via an operant procedure in which infants learned to perform a specific action (a footkick) to activate an object suspended before them. In Experiment 1, infants trained with different exemplars in the same context transferred responding to a novel exemplar in the same but not a different context 24 hours later. Experiment 2 revealed that infants' reactivated memory of category training remained intact and context-specific after 3 weeks. In Experiment 3, a novel category exemplar was able to reactivate the forgotten memory of category training only in the encoding context. At 6 months, information about the place where categories are constructed is prerequisite for retrieval of a category concept from long-term memory. This requirement insures that early category concepts remain stable over relatively long periods.

No abstract

We review the transport, fate, and bioavailability of mercury in the Sudbury River, topics addressed in the following five papers. Mercury entered the river from an industrial complex (site) that operated from 1917 to 1978. Rates of mercury accumulation in sediment cores from two reservoirs just downstream from the site decreased soon after industrial operations ended and have decreased further since capping of contaminated soils at the site in 1991. The reservoirs contained the most contaminated sediments (some exceeding 50 mg Hg·g dry weight -1 ) and were depositional sinks for total mercury. Methyl mercury concentrations in biota did not parallel concentrations of total mercury in the sediments to which organisms were exposed, experimentally or as residents. Contaminated wetlands within the floodplain about 25 km downstream from the site produced and exported methyl mercury from inorganic mercury that had originated from the site. Natural burial processes have gradually decreased the quantity of sedimentary mercury available for methylation within the reservoirs, whereas mercury in the lesser contaminated wetlands farther downstream has remained more available for transport, methylation, and entry into food webs.Résumé : Nous examinons le transport, le devenir et la biodisponibilité du mercure dans la rivière Sudbury, sujets qui sont traités dans les cinq articles qui suivent. Le mercure a pénétré dans la rivière pendant l'exploitation d'un complexe industriel (site) en service de 1917 à 1978. L'accumulation de mercure dans les carottes de sédiments de deux réser-voirs situés juste en aval du site a diminué peu après la cessation des activités industrielles et, depuis 1991, continue de diminuer depuis le recouvrement des sols contaminés de ce complexe. C'est dans les réservoirs que les sédiments étaient les plus contaminés (certains dépassant 50 mg Hg·g poids sec -1 ) et constituaient des puits pour le mercure total. Les concentrations de méthyl mercure dans le biote ne correspondaient pas aux concentrations de mercure total dans les sédiments auxquels les organismes ont été exposés, de façon naturelle et expérimentale. Les milieux humides contaminés de la plaine d'inondation, situés à environ 25 km en aval du site, produisaient et exportaient du méthyl mercure issu du mercure inorganique provenant du site. Les processus naturels d'enfouissement ont fait diminuer progressivement la quantité de mercure sédimentaire libre pour la méthylation dans les réservoirs, tandis que le mercure présent dans les milieux humides moins contaminés situés en aval était plus disponible pour le transport, la méthylation et l'entrée dans les réseaux trophiques.[Traduit par la Rédaction] Wiener and Shields 1061