One-trial associative memory in black-capped chickadees.

Black-capped chickadees (Parus atricapillus), birds that store food, inspected feeders in an aviary (1 of which was baited) and returned after a 5-min retention interval to consume the then-hidden food. In Exp 1, Ss quickly learned this task but only if different feeders were used on each trial. In Exp 2, memory for the baited feeder decayed substantially after 24 hrs but not after 30 min. In Exps 3 and 4, there were 4 alternatives to the baited feeder. Ss performed better than chance from the beginning of these experiments. When Ss made errors on their 1st choice, Ss performed better than chance on their 2nd choice. Exp 4 tested the notion that increasing the cost of inspecting the feeders would reduce errors; however, this did not improve performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Explaining category interference effects in associative memory.

Two studies with 220 undergraduates investigated the effects of categorization on the acquisition and long-term retention of AB word pairs using modeling techniques that factor the contributions of various storage and retrieval factors. In Exp I, each S memorized 1 of the 4 basic types of lists: unrelated cues/unrelated targets, categorized cues/unrelated cues, unrelated cues/categorized targets, and categorized cues/categorized targets. Ss in Exp II memorized 24-item AB lists to criterion. Acquisition data showed that there was a crossover interaction such that the effects of increasing the degree of cue or target relatedness depended on the nature of the comparison items. In contrast with the results of previous studies, the effects were larger when categorization was manipulated on the target side of AB pairs than when it was manipulated on the cue side. The degree of categorization affected retrieval difficulty but not storage difficulty. Long-term retention data indicated that, contrary to the acquisition data, the effects of categorization on retention were uniformly positive. Categorization decreased the amount of forgetting primarily by reducing the rate at which traces were lost from memory (storage failure) during the retention interval. Results are discussed in terms of modern unitary-trace theories of associative memory. (French abstract) (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adult age differences in memory performance: Tests of an associative deficit hypothesis.

An associative hypothesis to explain and predict older adults' deficient explicit episodic memory performance was outlined and tested. The hypothesis attributes a substantial part of older adults' deficient memory performance to their difficulty in merging unrelated attributes-units of an episode into a cohesive unit. Although each of the components can be memorized to a reasonable degree, the associations that tie the attributes-units to each other grow weaker in old age. Four experiments are reported that provide (a) a converging validity to the hypothesis by demonstrating this associative deficit for both interitem relationships and intraitem relationships and (b) a discriminant validity to the hypothesis by contrasting and testing competing predictions made by the associative hypothesis and by alternative hypotheses. The implications of these results to older adults' episodic memory performance are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separating bias and sensitivity in judgments of associative memory.

Ratings of the degree of association between words are linearly related to normed associative strengths, but the intercept is high, and the slope is shallow (the judgments of associative memory [JAM] function). Two experiments included manipulations intended to decrease the intercept and increase the slope. Discrimination training on many pairs of words and constraining ratings to sum to a constant both reduced the intercept but failed to change the slope. The intercept of the JAM function appears to contain a bias component that can be manipulated independently of the slope, which reflects sensitivity to associative strengths. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the nature of associative information in recognition memory.

In a typical associative-recognition task, participants must distinguish between intact word pairs (both words previously studied together) and rearranged word pairs (both words previously studied but as part of different pairs). The familiarity of the individual items on this task is uninformative because all of the items were seen before, so the only way to solve the task is to rely on associative information. Prior research suggests that associative information is recall-like in nature and may therefore be an all-or-none variable. The present research reports several experiments in which some pairs were strengthened during list presentation. The resulting hit rates and false alarm rates, and an analysis of the corresponding receiver operating characteristic plots, suggest that participants rely heavily on item information when making an associative-recognition decision (to no avail) and that associative information may be best thought of as a some-or-none variable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective attention in human associative learning and recognition memory.

Four experiments examined the role of selective attention in a new causal judgment task that allowed measurement of both causal strength and cue recognition. In Experiments 1 and 2, blocking was observed; pretraining with 1 cue (A) resulted in reduced learning about a 2nd cue (B) when those 2 cues were trained in compound (AB+). Participants also demonstrated decreased recognition performance for the causally redundant Cue B, suggesting that less attention had been paid to it in training. This is consistent with the idea that attention is preferentially allocated toward the more predictive Cue A, and away from the less predictive Cue B (e.g., N. J. Mackintosh, 1975). Contrary to this hypothesis, in Experiments 3 and 4, participants demonstrated poorer recognition for the most predictive cues, relative to control cues. A new model, which is based on N. J. Mackintosh's (1975) model, is proposed to account for the observed relationship between the extent to which each cue is attended to, learned about, and later recognized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Item and associative memory in amnestic mild cognitive impairment: Performance on standardized memory tests.

The earliest neuroanatomical changes in amnestic mild cognitive impairment (aMCI) involve the hippocampus and entorhinal cortex, structures implicated in the integration and learning of associative information. The authors hypothesized that individuals with aMCI would have impairments in associative memory above and beyond the known impairments in item memory. A group of 29 individuals with aMCI and 30 matched control participants were administered standardized tests of object-location recall and symbol-symbol recall, from which both item and associative recall scores were derived. As expected, item recall was impaired in the aMCI group relative to controls. Associative recall in the aMCI group was even more impaired than was item recall. The best group discriminators were measures of associative recall, with which the sensitivity and specificity for detecting aMCI were 76% and 90% for symbol-symbol recall and were 86% and 97% for object-location recall. Associative recall may be particularly sensitive to early cognitive change in aMCI, because this ability relies heavily on the medial temporal lobe structures that are affected earliest in aMCI. Incorporating measures of associative recall into clinical evaluations of individuals with memory change may be useful for detecting aMCI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preventing expulsive hemorrhage using an anterior chamber maintainer to eliminate hypotony

We describe a method in which constant infusion inflow through an anterior chamber maintainer (ACM) is used to maintain positive intraocular pressure (IOP) during cataract extraction through a self-sealing tunnel incision. A retrospective review of patient records showed that the difference in the incidence of intraoperative suprachoroidal hemorrhage was significantly greater in eyes in which IOP was not constant throughout surgery than in eyes in which IOP was maintained using the ACM system.     

Collaboration in associative recognition memory: Using recalled information to defend "new" judgments.

S. E. Clark, A. Hori, A. Putnam, and T. J. Martin (2000) showed that collaboration on a recognition memory task produced facilitation in recognition of targets but had inconsistent and sometimes negative effects regarding distractors. They accounted for these results within the framework of a dual-process, recall-plus-familiarity model but showed only weak evidence to support it. The present results of 3 experiments present stronger evidence for Clark et al.'s dual-process view and also show why such evidence is difficult to obtain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Professional expertise does not eliminate age differences in imagery-based memory performance during adulthood.

Using a testing-the-limits paradigm, the authors investigated the modulation (attenuation) of negative adult age differences in imagery-based memory performance as a function of professional expertise. Six older graphic designers, 6 normal older adults, 6 younger graphic design students, and 6 normal younger students participated in a 19-session program with a cued-recall variant of the Method of Loci. Older graphic designers attained higher levels of mnemonic performance than normal older adults but were not able to reach younger adults' level of performance; a perfect separation of age groups was achieved. Spatial visualization was a good predictor of mnemonic performance. Results suggest that negative adult age differences in imagery-based memory are attenuated but not eliminated by the advantages associated with criterion-relevant ability (talent) and experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-related deficits in associative memory: The influence of impaired strategic retrieval.

In 2 experiments, the authors investigated whether impaired strategic retrieval processes contribute to the age-related deficit in associative memory. To do so, they compared older and younger adults on measures of associative memory that place high demands on retrieval processes (associative identification and recall-to-reject) to measures that place low demands on such processes (associative reinstatement and recall-to-accept). Results showed that older adults were severely impaired on associative identification and recall-to-reject measures; relatively intact on recall-to-accept measures, unless recollection was prominent; and intact on associative reinstatement measures. Together, these findings suggest that impairment in strategic retrieval accounts for older adults' deficits in memory for associative information and that this deficit, above and beyond poor binding of items, leads to and amplifies an impairment in overall recollection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning attractors in an asynchronous, stochastic electronic neural network

LANN27 is an electronic device implementing in discrete electronics a fully connected (full feedback) network of 27 neurons and 351 plastic synapses with stochastic Hebbian learning. Both neurons and synapses are dynamic elements, with two time constants--fast for neurons and slow for synapses. Learning, synaptic dynamics, is analogue and is driven in a Hebbian way by neural activities. Long-term memorization takes place on a discrete set of synaptic efficacies and is effected in a stochastic manner. The intense feedback between the nonlinear neural elements, via the learned synaptic structure, creates in an organic way a set of attractors for the collective retrieval dynamics of the neural system, akin to Hebbian learned reverberations. The resulting structure of the attractors is a record of the large-scale statistics in the uncontrolled, incoming flow of stimuli. As the statistics in the stimulus flow changes significantly, the attractors slowly follow it and the network behaves as a palimpsest--old is gradually replaced by new. Moreover, the slow learning creates attractors which render the network a prototype extractor: entire clouds of stimuli, noisy versions of a prototype, used in training, all retrieve the attractor corresponding to the prototype upon retrieval. Here we describe the process of studying the collective dynamics of the network, before, during and following learning, which is rendered complex by the richness of the possible stimulus streams and the large dimensionality of the space of states of the network. We propose sampling techniques and modes of representation for the outcome.     

Impairment of long-term associative memory in aging snails (Lymnaea stagnalis).

Age-dependent impairment in learning and memory functions occurs in many animal species, including humans. Although cell death contributes to age-related cognitive impairment in pathological forms of aging, learning and memory deficiencies develop with age even without substantial cell death. The molecular and cellular basis of this biological aging process is not well understood but seems to involve a decline in the aging brain's capacity for experience-dependent plasticity. To aid in resolving this issue, we used a simple snail appetitive classical conditioning paradigm in which the underlying molecular, cellular, and neural network functions can be directly linked to age-associated learning and memory performance (i.e., the Lymnaea stagnalis feeding system). Our results indicate that age does not affect the acquisition of appetitive memory but that retention and/or consolidation of long-term memory become progressively impaired with advancing age. The latter phenomenon correlates with declining electrophysiological excitability in key neurons controlling the feeding behavior. Together, these results present the Lymnaea feeding system as a powerful paradigm for investigations of cellular and molecular foundations of biological aging in the brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context and mediators in a theory of distributed associative memory (TODAM2).

Recent findings on the interactions of item and associative information have necessitated a revision of TODAM (a theory of distributed associative memory). Item information underlies the memory for individual items or events, and associative information allows one to relate or associate 2 separate items or events. The troublesome findings are the differential forgetting of item and associative information (item recognition falls off over retention intervals, whereas associative information does not) and the differential emphasis results (greater attention to items hurts pair recognition, but greater attention to pairs does not affect item recognition). The addition of context and mediators enables TODAM to account for these interactions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of an amygdalo-nigrostriatal pathway in associative learning

The present study examined the role of an amygdalo-nigrostriatal pathway in associative learning. An asymmetrical lesion model was used to test whether a circuit from the amygdala central nucleus to the dorsolateral striatum, via the substantia nigra, is critical for mediating conditioned orienting responses. Rats with an asymmetrical lesion, consisting of neurotoxic removal of central nucleus neurons in one hemisphere and depletion of the dopamine innervation of the dorsolateral striatum in the contralateral hemisphere, failed to acquire conditioned orienting responses. In contrast, the asymmetrical lesion had no effect on spontaneous orienting or learning another response directed to the source of the food unconditioned stimulus in the same task. A second experiment tested the effect of reversible inactivation of the dorsolateral striatum contralateral to a neurotoxic central nucleus lesion on acquisition of the conditioned orienting response. Although inactivation did not affect spontaneous orienting, rats failed to acquire the conditioned orienting response during sessions in which inactivation occurred. Immediately after the inactivation procedure was terminated, however, a significant increase in orienting to the conditioned stimulus was evident. These data support the interpretation that the dorsolateral striatum provides a route for the expression of the conditioned orienting response but is not essential for acquisition of this learned behavior.     

Neurite growth patterns leading to functional synapses in an identified embryonic neuron

We explored the relationship between neurite outgrowth and the onset of synaptic activity in the central neuropil of the leech embryo in vivo. To follow changes in early morphology and the onset of synaptic activity in the same identified neuron, we obtained whole-cell patch-clamp recordings and fluorescent dye fills from dorsal pressure-sensitive (P) cells, the first neurons that could be reliably identified in the early embryo. We followed the development of the P cell from the first extension of neurites to the elaboration of an adult-like arbor. After the growth of primary neurites, we observed a profuse outgrowth of transient neurites within the neuropil. Retraction of the transient neurites left the primary branches studded with spurs. After a dormant period, stable secondary branches grew apparently from the spurs and became tipped with terminals. At this time, neurites of the Retzius (R) cell, a known presynaptic partner in the adult, were observed to apparently contact the terminals. Although voltage-dependent currents were seen in the P cell at the earliest stage, spontaneous synaptic activity was only observed when terminals had formed. Spontaneous release was observed before evoked release could be detected from the R cell. Our results suggest that transient neurites are formed during an exploratory phase of development, whereas the more precisely timed outgrowth of stable neurites from the spurs signals functional differentiation during synaptogenesis. Because spurs have also been observed in neurons of the mammalian brain, they may constitute a primordial synaptic organizer.