Werner Wippich

Selective amnesic effects of oxytocin on human memory

The neuropeptide oxytocin is essential for mammalian parturition and lactation. Recent animal studies suggest that oxytocin is also implicated in the central nervous control of behavior including learning and memory. There has been little investigation, however, of the impact of oxytocin on human memory. The purpose of this study was to investigate the effect of a single dose of intranasal oxytocin on implicit and explicit memory in humans. In a placebo-controlled, double-blind study, 38 healthy men were randomly assigned to receive intranasal oxytocin (24 IU) or placebo 50 min before the study phase (incidental learning). Memory was measured using three different memory tests: an implicit perceptual test (word stem completion), an implicit conceptual test (category-cued semantic association), and an explicit test (cued recall). Due to the reproductive-biological role of oxytocin and the impact of adequate environmental conditions for the stimulation of behavioral effects of oxytocin known from animal research, we used semantic word stimuli with reproduction-related vs. neutral meaning. Oxytocin significantly impaired recall performance as compared with placebo treatment irrespective of the meaning of words in the cued recall test. In the implicit conceptual test, characterized by a deepened information processing, compared with placebo, oxytocin significantly impaired only the overall generation of associated target words with reproduction relevant meaning, whereas no significant difference between oxytocin and placebo was obtained for neutral words. These findings concur with data from animal research suggesting that central oxytocin selectively influences memory performance depending on the kind of memory test used and, more importantly, the psychobiological relevance of stimuli.

On the reliability of implicit and explicit memory measures.

Functional dissociations between implicit and explicit memory tests often take the form of large differences between groups or experimental conditions (e.g., amnesics and controls, elderly and younger persons, or persons learning with and without a distracting secondary task) when performance is assessed using explicit memory tests, whereas no difference is observed with implicit memory tests. We argue that the interpretation of such dissociations in terms of the memory processes or systems involved in performance is problematic because the same data pattern would emerge as a result of a mere methodological artifact, that is, the situation that implicit memory tests have low reliability whereas explicit memory tests are fairly reliable measurement instruments. We present reasons for such a reliability difference, and we demonstrate it empirically in Experiments 1a, 1b, and 2. However, our analysis also shows, and Experiment 3 confirms empirically, that implicit memory tests need not necessarily be less reliable measurement instruments than explicit memory tests.

Age-related improvements in a conceptual implicit memory test.

The present study investigated developmental improvements in category exemplar generation priming in children from kindergarten to older elementary school age. The strength of categorical links for atypical exemplars increases in this age range, whereas category knowledge for typical exemplars remains relatively stable. Therefore, in comparison with older children, younger children should show less categorical-relational encoding and, thus, less priming for atypical items but not for typical items. This expectation was confirmed in Experiment 1. In Experiment 2, picture versus word format at study dissociated implicit and explicit performance, indicating that the age-related increase in priming for atypical exemplars in Experiment 1 was not an artifact of explicit contamination. The findings suggest that developmental improvements in conceptual priming can be observed when the conceptual knowledge relevant for a given task improves over the age range tested.

What colour is the car? Implicit memory for colour information in children:

Three experiments were conducted to examine age-related differences in colour memory. In Experiment 1, preschool age and elementary school age children were given a conceptual test of implicit colour memory (a colour-choice task). They were presented with the names or achromatic versions of previously studied coloured line drawings and asked to select an appropriate colour. Significant priming could be demonstrated: The children chose the previously seen colours more often than was expected by chance. Equivalent priming was found for both versions (pictorial and verbal) suggesting that colour priming may be conceptually mediated. Moreover, colour priming proved to be age invariant. Experiment 2 replicated and extended this finding by using a wider age group (preschool, elementary school, and young adults) and by giving a perceptual implicit task (picture identification) in addition to a verbal colour-choice task. Colour did not affect priming in the perceptual task. Whereas priming showed no developmental change, age related improvements were observed on an explicit colour memory task that differed only in the test instructions from the implicit colour-choice task (Experiments 2 and 3). Taken together, the results suggest that implicit colour memory may be mediated by conceptual processes that are age invariant.

Implicit and explicit memory without awareness

SummaryThree experiments are reported which investigate the conscious status of subjects during an implicit-memory test. In all experiments the subjects either named each visually presented target item or generated each item from an anagram in a first phase of incidental learning. In a second phase, they were either given a visual word-stem completion task as an implicit-memory test or given a recognition task (Experiment 1), or a cued-recall task (Experiments 2 and 3) as explicit-memory tests. Finally, in a third phase the subjects were required to make decisions about the input status (i. e., they had to decide whether the item was present in the first phase) as well as about the output status of information (i. e., they had to decide whether the item had been completed, recognized or recalled in the second phase). A generation effect (i. e., generated items were remembered better than named items) was evident in the recognition and recall data, but only for items whose recognition or recall was accompanied by conscious recollection of their previous occurrence in the study list. Judgments about the input status were more precise, given that items had been consciously recognized or recalled rather than completed. The same pattern of findings was observed for judgments about the output status. The results are interpreted as evidence that subjects in implicit-memory tests are less aware of the fact that some of their productions are relevant to prior experiences. In addition, they are less aware of the fact that they are retrieving information from their memories. However, the same state of nonawareness may be present in explicit-memory tests, as was revealed by the performance of subjects on those items whose recognition or recall was not accompanied by conscious recollection.

Implicit memory for textual materials

As a word moves from isolation in a list to being contextually bound in meaningful discourse, its probability of priming in tests of implicit memory decreases. The present experiments explore whether considerable priming effects can be revealed with conceptual tests of implicit memory as compared to perceptual tests. In the study phase, meaningful actions were described within a coherent text. In Experiment 1 subjects elaborated half of the actions by visual imagery. In Experiment 2, subjects elaborated the actions by enacting them symbolically. In both experiments, subjects in a control condition were simply required to read the same activities. In Experiment 2, a further group of subjects had to detect orthographic errors. The results demonstrated reliable effects of implicit memory in terms of associations with verbs repeated from the studied text. This form of repetition priming for textual materials in a conceptual test of implicit memory was enhanced by both types of elaboration. A word-stem completion task for the same targets revealed a less pronounced and inconsistent priming effect, uninfluenced by both types of elaboration. But the latter form of perceptual priming was found to be more pronounced within the error-detection condition. Measures of explicit memory showed similar effects of elaborative encoding conditions but there were some dissimilarities to measures of implicit memory, too. In general and in accordance with a transfer-appropriate processing view, conceptual tests rather than perceptual tests may be more suitable for detecting effects of implicit memory within the domain of text processing.

Priming on verbal perceptual tests: Roles of lexical, surface, and conceptual processes

According to a lexical-access hypothesis, priming on verbal-completion tests requires previous access to higher-order nodes such as morphemes or words. In two experiments, subjects studied words presented in printed color, either by reading the words or by naming the printed colors. In Experiment 2, some of the words were to be ignored in both study conditions. The words presented in Experiment 2 were either conceptually related or unrelated to each other. And the cues in the test phase for repeated targets were either printed in the studied color or in a different color. In both experiments, the word stems of nouns studied and of new targets were presented with word-completion instructions (implicit test of memory). Consistent with the hypothesis, the amount of priming obtained was greater in the reading than in the color-naming condition. The least amount of priming was observed for targets that were to be ignored at study. In addition, Experiment 2 showed considerable effects of surface similarity (i.e., stronger priming effects with cues whose color was not changed from the study to the test phase) and some effects of conceptual processing, as was indicated by different amounts of priming for unrelated and for related nouns. Because these two effects were observed with both types of study task, it is concluded that perceptual and conceptual processes may make independent contributions to priming effects in verbal perceptual tests. This conclusion modifies and extends the original hypothesis, according to which previous lexical access is required in order to obtain effects of perceptual or conceptual processes on the priming scores.

Intuition in the context of implicit memory

SummaryMost recent work concerned with intuition has demonstrated that people can respond discriminatively to coherence that they cannot identify. Specifically, in a gestalt-closure task subjects were shown slides of paired drawings. One of the drawings represented a fragmented picture of a common object, whereas the other was constructed by rotation of the elements of the coherent gestalt. When the subjects were unable to name the object, they were urged to make a forced-choice decision regarding which of the two drawings represented a real object. The results showed that the proportion of pictures not correctly identified, that were nevertheless correctly selected as coherent, was significantly higher than chance. The current experiment replicated these findings. In addition, it was shown that a study phase with either coherent or incoherent picture primes can bias intuitive judgments in the test phase in accordance with a processing view. Incoherent-picture primes reduced the forced-choice decisions to a level of chance. Moreover, priming was found to be dependent on the similarity between the study and the test stimuli. We argue that a more fluent reprocessing of coherent, or primed, stimuli may be a basis for intuitive judgments. Intuition may go wrong when priming has favored an incoherent solution.

Spatial Information and Actions

The present study investigates connections between spatial information and actions. Only a few studies on this topic have been published to date. Moreover, changes in spatial representations have not been examined following the connection with actions. Our results show that previously acquired spatial information (i.e., information about locations along a learned route) can be associated with imagined or with symbolically performed actions. However, we have not yet found any evidence that spatial representations are altered by the formation of these associations. We conclude that more sensitive and, perhaps, implicit measures of spatial representations are needed in order to detect the presumed action-dependent changes. Furthermore, the salience of the actions and their connection to the spatial environment should be considered as important variables.

Haptic information processing in direct and indirect memory tests

SummaryEffects of learning can show up in a direct, i. e., an explicit, way or they can be expressed indirectly, i. e., in an implicit way. It was investigated whether motor processes underlie effects of repetition priming in haptic information exploration. In the test phase, blindfolded subjects had to handle objects in order to answer questions as fast as possible about their properties (e.g., temperature, texture, weight, or form), exploring the object with their hands. Some of the objects were old ones (presented in a study phase); others were added as new objects to the test phase. In addition, recognition judgements were required. The results demonstrated reliable effects of repetition priming in terms of reaction times to old, in comparison with new, objects for subjects who had been treated the same way in the study phase (active touch). Passive touch at encoding or studying the names or the visible objects themselves did not lead to effects of repetition priming in the test phase. On the other hand, performing adequate hand movements during the study improved recognition memory. The role of motor processes in indirect and direct tests of memory is discussed and related to research on memory of action events.