Distinct Memory Systems Research Articles

Recognition memory and decision processes: A meta-analysis of remember, know, and guess responses

A meta-analysis of proportions of remember, know, and guess responses was carried out on observations from 86 experimental conditions in 23 different recognition memory experiments. Unlike remember and know responses, guess responses revealed no memory for the test items that elicited them. A signal detection analysis of these data showed that A′ estimates of the strength of the memory trace depended on response criteria. A′ estimates increased significantly when know responses were added to remember responses, and decreased significantly when guess responses were added to remember and know responses. It was guessing, rather than knowing, that was most strongly correlated with overall response criteria. Nor were remembering and knowing correlated significantly. These results do not support a quantitative trace strength model according to which these responses merely reflect different response criteria. They support theories that ascribe remembering and knowing to qualitatively distinct memory systems or processes.

A dissociation in infants' memory for stimulus size: evidence for the early development of multiple memory systems.

Adults' memory performance on recognition (explicit memory) tests is sensitive to stimulus size, but their performance on priming (implicit memory) tests is not. This memory dissociation is taken as evidence for two, functionally distinct memory systems. Young infants, however, are thought to possess only a single representational system that supports implicit memory; the system that supports explicit memory is thought not to mature before 8-9 months of age. In two experiments with 54 infants, we asked if 3-month-olds exhibit a memory dissociation for stimulus size on recognition and priming tests. All infants learned to move a mobile displaying +s of a given size. In Experiment 1, infants recognized +s in the original size but not 33% smaller or larger. In Experiment 2, +s were effective memory primes in a reactivation task, irrespective of size. The finding that young infants exhibit a memory dissociation for stimulus size adds to growing evidence that two memory systems are functional from early in development.

Dissociative Effects of Alcohol on Recollective Experience

This article reports a study comparing the effects of a single dose of alcohol with a matched placebo drink on recognition memory with and without conscious recollection. A double-blind, cross-over design was used with healthy volunteers who were all social drinkers. Processing depth at study was manipulated using generate versus read instructions. Conscious recollection at test was assessed using the remember–know–guess paradigm (Gardiner, 1988; Tulving, 1985). Alcohol significantly reduced conscious recollection (remember responses) but had no effect on recognition in the absence of conscious recollection (know responses). False alarms rates were low and unaffected by alcohol. Previous findings that generation effects are found only for remember responses were closely replicated. A further dissociation of the generation effect occurred between treatments in that deeper processing at study facilitated recognition on placebo but not on alcohol. That both alcohol and depth of processing produce dissociative effects on recollective experience provides further evidence that remembering and knowing reflect distinct memory systems.

Estrategias de aprendizaje espacial en la carpa dorada (Carassius auratus).

Mammals and birds can use different spatial navigation strategies subserved by distinct learning and memory systems. A range of evidence suggests that, when animals are trained in a test environment where they can simultaneously rely on the spatial relationships among distal landmarks (place strategy) and on a single conspicuos local visual cue (cue strategy) to find a goal, they learn both place and cue strategies to solve the task. However, despite the importance of comparative studies for understanding the structure and function of spatial learning and memory systems in vertebrates, only a few studies have investigated spatial learning mechanisms in other vertebrate groups, such as fish. This experiment was designed to study the spatial strategies used by goldfish to find a goal in a plus maze. Goldfish were trained to find food in an arm placed in a constant room location and simultaneusly signaled by a single local visual cue (mixed place-cue procedure). Later probe trials were performed in order to to examine the relative importance of these sources of information and reveal learning and memory strategies used by the animals to solve the maze task. In these probe trials, either the two sources of information were dissociated in such a way that the goldfish needed to choose between place or guidance responses, or intramaze proximal cues or the extramaze distal landmarks were individually removed. The results suggest that fish, like mammals and birds, are able to solve a maze task using a place strategy ora guidance Strategy, and that these animals can switch from one strategy to another choosing and correctly performing the more adecuate of the two in each situation.

Infants' Memory Processing of a Serial List: List Length Effects

Six-month-olds, trained with a three-mobile serial list, exhibit a primacy effect 24 h later. In three experiments, we demonstrated that increasing list length impairs their memory for serial order. In all experiments, 6-month-olds were trained with a five-mobile list. In Experiment 1, infants failed to exhibit a primacy effect on a 24-h delayed recognition test, recognizing mobiles from all serial positions. In Experiment 2, infants did exhibit a primacy effect on a reactivation (priming) test, suggesting that they may originally have encoded serial-order information. Experiment 3 confirmed that serial-order information was represented in infants' training memory. After the reactivation treatment, infants were precued with one list member and tested for recognition of another. When precues specified valid order information, infants recognized test mobiles from the later serial positions. The memory dissociation for serial order on delayed recognition and reactivation tests adds to the growing evidence that young infants possess two functionally distinct memory systems.

Distinct short-term memory systems for sound content and sound localization.

Short-term memory for sound content and sound localization was investigated in normal subjects using the same/different comparison of two sound stimuli separated by an interval. Auditory or visual interference tasks requiring recognition or spatial judgements were introduced in the interval. Auditory interference tasks reduced memory for sound content and sound location in a specific way. Memory for sound content was significantly more reduced by auditory recognition than by auditory spatial interference task. Visual interference tasks reduced significantly memory for sound location but not for sound content. These results suggest that (i) short-term memory for sound content and that for sound location involve partially distinct processing; and (ii) auditory spatial functions are more closely linked to visual functions than auditory recognition.

Associative and perceptual learning and the concept of memory systems

An introductory review is followed by some new experimental data and a final discussion. The primate temporal lobe contains multiple qualitatively distinct memory systems. The functional properties of these memory systems can be explained by reference to the nature of the afferent information which they process, rather than by reference to any putative specialization in memory processing. In this way, the plasticity of `memory systems' in associative memory is probably similar in principle to the plasticity of `perceptual systems' in perceptual learning. Therefore, it is important to consider the relationship between perceptual and associative learning. Two experiments investigated perceptual learning in the Rhesus monkey ( Macaca mulatta). Substantial perceptual learning was observed both with complex scenes and with simple colours. Two hypotheses as to the basis of perceptual learning are discussed. A physiological hypothesis is that training with a particular set of stimuli expands the cortical representation of those stimuli. This can explain the effects in both experiments. A psychological hypothesis is that perceptual learning is produced by learned associations among the multiple features of complex stimuli. This can explain the effects in Expt. 1 but not in Expt. 2. The psychological associative hypothesis is therefore redundant. Furthermore, associative learning can itself be viewed as an expansion of the cortical representation of a complex event. Thus, the distinction between perceptual and memory systems will need to be abandoned as deeper understanding of cortical plasticity is achieved.

Differential effects of fornix and caudate nucleus lesions on two radial maze tasks: evidence for multiple memory systems

The present experiments were designed to examine the hypothesis that the mammalian brain contains anatomically distinct memory systems. Rats with bilateral lesions of caudate nucleus or fimbria-fornix and a control group were tested postoperatively on 1 of 2 versions of the radial maze task. In a standard win-shift version, each of the 8 arms of the maze was baited once, and the number of errors (revisits) in the first 8 choices of each trial was recorded. Fimbria-fornix rats were impaired in choice accuracy, while caudate animals were unimpaired relative to controls. Different groups of rats with similar lesions were tested on a newly developed win-stay version of the radial maze, in which the location of 4 randomly selected baited arms was signaled by a light at the entrance to each arm, and which required rats to revisit arms in which reinforcement had been previously acquired within a trial. Rats with fimbria-fornix lesions were superior to controls in choice accuracy on the win-stay radial maze task, while caudate animals were impaired relative to controls. The results demonstrate a double dissociation of the mnemonic functions of the hippocampus and caudate nucleus. Some implications of the presence of 2 memory systems in the mammalian brain are discussed.