The Accuracy of Causal Learning Over Long Timeframes: An Ecological Momentary Experiment Approach

The ability to learn cause–effect relations from experience is critical for humans to behave adaptively — to choose causes that bring about desired effects. However, traditional experiments on experience-based learning involve events that are artificially compressed in time so that all learning occurs over the course of minutes. These paradigms therefore exclusively rely upon working memory. In contrast, in real-world situations we need to be able to learn cause–effect relations over days and weeks, which necessitates long-term memory. 413 participants completed a smartphone study, which compared learning a cause–effect relation one trial per day for 24 days versus the traditional paradigm of 24 trials back- to- back. Surprisingly, we found few differences between the short versus long timeframes. Subjects were able to accurately detect generative and preventive causal relations, and they exhibited illusory correlations in both the short and long timeframe tasks. These results provide initial evidence that experience-based learning over long timeframes exhibits similar strengths and weaknesses as in short timeframes. However, learning over long timeframes may become more impaired with more complex tasks.     

Age-Related Differences in Memory Illusions: Revelation Effect

Older adults are often more susceptible to various illusions and distortions of memory than young adults. In the experiments reported here, we explored the question of whether normal aging was associated with a larger revelation effect, an illusion of memory in which items that are revealed gradually during a recognition test are more likely to be called old than unrevealed items that are shown in their entirety. Contrary to expectations, older adults were not susceptible to this memory illusion. A revelation effect occurred for young but not older adults, even when older adults were similar to young adults on measures of recognition and repetition priming. When data across experiments were combined, there was evidence for a negative revelation effect in older adults in which revealed items were less likely called old than unrevealed items. These results place boundary conditions on the claim that older adults are more susceptible than young adults to memory illusions, and imply that one or more mechanisms underlying the revelation effect are age sensitive.     

The Role of Long-Term Memory in Digit–Symbol Test Performance in Young and Older Adults

ABSTRACT

The psychological functions assessed by substitution tests, and the age-related performance decline, are not well understood. Here several aspects of long-term memory were manipulated across younger and older adults. A 45-page Digit–Symbol test was employed. Each page contained a 9-item digit symbol code-table and 9 response items. There were 9 study conditions with each condition deployed across 5 pages, or trials, of the test. The conditions were formed by crossing two within-subjects factors, each with 3 levels. The first factor, Digit Order, pertained to having the code table digits in numerical order vs. a pseudo-random order fixed across trials vs. a pseudo-random order that varied across trials. The second factor, Symbol Pairing, pertained to having a fixed digit–symbol pairing across trials vs. having a varying digit–symbol pairing across trials vs. having a novel set of 9 symbols introduced on each of the 5 trials. Including the additional factor, Age, resulted in a 2 × 3 × 3 mixed randomised block design. The older group was slowed, F(1, 22) = 17.267, p < .001, and overall-performance was poorer when the digits were arranged non-numerically, F(1,44) = 55.403, p < .001. An Age by Symbol–Order interaction indicated that use of novel symbols disadvantaged only the older participants, F(1, 44) = 6.577, p = .014. While there was no evidence that incidental paired-associate learning or spatial memory affect digit–symbol performance, symbol familiarity may be important to digit symbol test completion in older adults. The benefit of ordinally arranged digits in the coding table highlights a fundamental process difference between Digit–Symbol and Symbol–Digit test formats.     

Memory for emotionally provocative words in alexithymia: A role for stimulus relevance

Alexithymia is associated with emotion processing deficits, particularly for negative emotional information. However, also common are a high prevalence of somatic symptoms and the perception of somatic sensations as distressing. Although little research has yet been conducted on memory in alexithymia, we hypothesized a paradoxical effect of alexithymia on memory. Specifically, recall of negative emotional words was expected to be reduced in alexithymia, while memory for illness words was expected to be enhanced in alexithymia.Eighty-five high or low alexithymia participants viewed and rated arousing illness-related (“pain”), emotionally positive (“thrill”), negative (“hatred”), and neutral words (“horse”). Recall was assessed 45 min later.High alexithymia participants recalled significantly fewer negative emotion words but also more illness-related words than low alexithymia participants. The results suggest that personal relevance can shape cognitive processing of stimuli, even to enhance retention of a subclass of stimuli whose retention is generally impaired in alexithymia.     

Co-induction of long-term potentiation and long-term depression at a central synapse in the leech

Most studies of long-term potentiation (LTP) have focused on potentiation induced by the activation of postsynaptic NMDA receptors (NMDARs). However, it is now apparent that NMDAR-dependent signaling processes are not the only form of LTP operating in the brain [Malenka, R. C., & Bear, M. F. (2004). LTP and LTD: An embarrassment of riches. Neuron, 44, 5–21]. Previously, we have observed that LTP in leech central synapses made by the touch mechanosensory neurons onto the S interneuron was NMDAR-independent [Burrell, B. D., & Sahley, C. L. (2004). Multiple forms of long-term potentiation and long-term depression converge on a single interneuron in the leech CNS. Journal of Neuroscience, 24, 4011–4019]. Here we examine the cellular mechanisms mediating T-to-S (T → S) LTP and find that its induction requires activation of metabotropic glutamate receptors (mGluRs), voltage-dependent Ca²⁺ channels (VDCCs) and protein kinase C (PKC). Surprisingly, whenever LTP was pharmacologically inhibited, long-term depression (LTD) was observed at the tetanized synapse, indicating that LTP and LTD were activated at the same time in the same synaptic pathway. This co-induction of LTP and LTD likely plays an important role in activity-dependent regulation of synaptic transmission.     

Habituation in Aplysia: The Cheshire Cat of neurobiology

The marine snail, Aplysia californica, is a valuable model system for cell biological studies of learning and memory. Aplysia exhibits a reflexive withdrawal of its gill and siphon in response to weak or moderate tactile stimulation of its skin. Repeated tactile stimulation causes this defensive withdrawal reflex to habituate. Both short-term habituation, lasting <30 min, and long-term habituation, which can last >24 h, have been reported in Aplysia. Habituation of the withdrawal reflex correlates with, and is in part due to, depression of transmission at the monosynaptic connection between mechanoreceptive sensory neurons and motor neurons within the abdominal ganglion. Habituation-related short-term depression of the sensorimotor synapse appears to be due exclusively to presynaptic changes. However, changes within the sensory neuron, by themselves, do not account for more persistent depression of the sensorimotor synapse. Recent behavioral work suggests that long-term habituation in Aplysia critically involves postsynaptic processes, specifically, activation of AMPA- and NMDA-type receptors. In addition, long-term habituation requires activity of protein phosphatases, including protein phosphatases 1, 2A, and 2B, as well as activity of voltage-dependent Ca²⁺ channels. Cellular work has succeeded in demonstrating long-term, homosynaptic depression (LTD) of the sensorimotor synapse in dissociated cell culture and, more recently, LTD of the glutamate response of isolated motor neurons in culture (“hemisynaptic” LTD). These in vitro forms of LTD have mechanistic parallels to long-term habituation. In particular, homosynaptic LTD of the sensorimotor synapse requires elevated intracellular Ca²⁺ within the motor neuron, and hemisynaptic LTD requires activity of AMPA- and NMDA-type receptors. In addition, activation of group I and II metabotropic glutamate receptors (mGluRs) can induce hemisynaptic LTD. The demonstration of LTD in vitro opens up a promising new avenue for attempts to relate long-term habituation to cellular changes within the nervous system of Aplysia.     

Impaired long-term potentiation and enhanced neuronal excitability in the amygdala of CaV1.3 knockout mice

Previously, we demonstrated that mice in which the gene for the L-type voltage-gated calcium channel Ca_V1.3 is deleted (Ca_V1.3 knockout mice) exhibit an impaired ability to consolidate contextually-conditioned fear. Given that this form of Pavlovian fear conditioning is critically dependent on the basolateral complex of the amygdala (BLA), we were interested in the mechanisms by which Ca_V1.3 contributes to BLA neurophysiology. In the present study, we used in vitro amygdala slices prepared from Ca_V1.3 knockout mice and wild-type littermates to explore the role of Ca_V1.3 in long-term potentiation (LTP) and intrinsic neuronal excitability in the BLA. We found that LTP in the lateral nucleus (LA) of the BLA, induced by high-frequency stimulation of the external capsule, was significantly reduced in Ca_V1.3 knockout mice. Additionally, we found that BLA principal neurons from Ca_V1.3 knockout mice were hyperexcitable, exhibiting significant increases in firing rates and decreased interspike intervals in response to prolonged somatic depolarization. This aberrant increase in neuronal excitability appears to be at least in part due to a concomitant reduction in the slow component of the post-burst afterhyperpolarization. Together, these results demonstrate altered neuronal function in the BLA of Ca_V1.3 knockout mice which may account for the impaired ability of these mice to consolidate contextually-conditioned fear.     

Long-term memory for categories and concepts in horses (Equus caballus)

Three horses (Equus caballus) with a history of performing cognitive tasks including discrimination learning, categorization, and concept use were tested to evaluate their long-term memory (LTM) in three experiments. In addition, use of LCD multi-displays for stimulus presentation was incorporated into cognition testing protocol for the first time with horses. Experiment 1 tested LTM for discrimination learning that originally occurred 6 years earlier. Five sets of stimuli were used and the two horses tested showed no decrement in performance on four of the sets; however, both horses did score below chance on one set. Experiment 2 examined long-term categorization recall 10 years after horses had demonstrated the ability to make stimulus selections based on shared characteristics within a given category. The horse tested for LTM after the decade-long interval immediately and consistently applied the previously learned categorization rule to not only familiar but also novel sets of stimuli. Experiment 3 tested another horse for LTM for a relative size concept. This horse had originally demonstrated concept rule use in order to select stimuli based on their relative size to one another. More than 7 years later and without further training, this horse reliably applied the previously established size concept to both familiar and novel sets of stimuli. These findings are the first reports of long-term categorical and conceptual memory in horses and are consistent with observations of domestic and wild horses, which indicate that behavioral and ecological events may be remembered for long periods of time. These studies also demonstrate the adaptive nature of horses with regard to their ability to generalize over several different testing conditions.     

Mixing against culture vs mixing against nature: ontologization of prohibited interethnic relationships

In this paper, we develop the theory of ontologization: Social representations that prevent members of minority and majority groups who are living in contact with each other to mingle. The process of ontologization consists of separating some humans from their own species, and anchoring them in another environment, that of an animal, for example. We propose that underlying the famous slogan “equal but separate” is the social representation of interracial mixing as a “counter‐nature” phenomenon. It is predicted that a sexual relationship between people of different “races” leads to a greater degree of ontologization, and, as such, this miscegenation will be explained in terms of biologistic thinking, like an instinctive nature or atavistic animal impulse. An experiment (N = 360) features the case of a woman who, though already in a stable relationship, is unfaithful to her partner. In a 2×3 factor design, the ethnic‐national identity of this woman (in‐group: Spanish/Italian vs out‐group: Senegalese) and the ethnic‐national identity of her lovers (in‐group: Spanish/Italian vs out‐group: Rumanian vs out‐group: Senegalese) were manipulated. In general, results fit the hypothesis of ontologization in interracial conditions better, rather than the customary in‐group favouritism and/or out‐group discrimination bias. We then go on to discuss the way in which a biologistic way of thinking enables a differentiation at the human level, in terms of culture groups and nature groups, in “races,” so that an interracial sexual relationship is seen as evidence of a wild and irrepressible impulse, which stigmatizes the people involved in these relationships.