The impact of auditory distraction on retrieval of visual memories

Recent research has revealed that the presence of irrelevant visual information during retrieval of long-term memories diminishes recollection of task-relevant visual details. Here, we explored the impact of irrelevant auditory information on remembering task-relevant visual details by probing recall of the same previously viewed images while participants were in complete silence, exposed to white noise, or exposed to ambient sounds recorded at a busy café. The presence of auditory distraction diminished objective recollection of goal-relevant details, relative to the silence and white noise conditions. Critically, a comparison with results from a previous study using visual distractors showed equivalent effects for auditory and visual distraction. These findings suggest that disruption of recollection by external stimuli is a domain-general phenomenon produced by interference between resource-limited, top-down mechanisms that guide the selection of mnemonic details and control processes that mediate our interactions with external distractors.     

Amygdala responses to emotionally valenced stimuli in older and younger adults

Abstract— As they age, adults experience less negative emotion, come to pay less attention to negative than to positive emotional stimuli, and become less likely to remember negative than positive emotional materials. This profile of findings suggests that, with age, the amygdala may show decreased reactivity to negative information while maintaining or increasing its reactivity to positive information. We used event-related functional magnetic resonance imaging to assess whether amygdala activation in response to positive and negative emotional pictures changes with age. Both older and younger adults showed greater activation in the amygdala for emotional than for neutral pictures; however, for older adults, seeing positive pictures led to greater amygdala activation than seeing negative pictures, whereas this was not the case for younger adults.     

Strong memories are hard to scale

People are generally skilled at using a confidence scale to rate the strength of their memories over a wide range. Specifically, low-confidence recognition decisions are often associated with close-to-chance accuracy, whereas high-confidence recognition decisions can be associated with close-to-perfect accuracy. However, using a 20-point rating scale, the authors found that the ability to scale memory strength had its limitations in that a high proportion of list items received the highest rating of 20. Efforts to induce participants to differentiate between these strong memories using emphatic instructions and alternative scales were not successful. Remember/know judgments indicated that these strong and hard-to-scale memories were often based on familiarity (not just recollection). Providing error feedback on a plurals discrimination task finally produced a high-confidence criterion shift. The authors suggest that the ability to scale strong (and almost perfectly accurate) memories may be limited because of the absence of differential error feedback for very strong memories in the past (the kind of differential error feedback that may account for the memory-scaling expertise that participants otherwise exhibit).     

Recollection Is a Continuous Process: Implications for Dual-Process Theories of Recognition Memory

ABSTRACT— Dual-process theory, which holds that recognition decisions can be based on recollection or familiarity, has long seemed incompatible with signal detection theory, which holds that recognition decisions are based on a singular, continuous memory-strength variable. Formal dual-process models typically regard familiarity as a continuous process (i.e., familiarity comes in degrees), but they construe recollection as a categorical process (i.e., recollection either occurs or does not occur). A continuous process is characterized by a graded relationship between confidence and accuracy, whereas a categorical process is characterized by a binary relationship such that high confidence is associated with high accuracy but all lower degrees of confidence are associated with chance accuracy. Using a source-memory procedure, we found that the relationship between confidence and source-recollection accuracy was graded. Because recollection, like familiarity, is a continuous process, dual-process theory is more compatible with signal detection theory than previously thought.     

An improved screw-free method for electrode implantation and intracranial electroencephalographic recordings in mice

We recently developed a glue-based method for the implantation of intracranial electrodes in mice. Our approach is to secure a preconstructed electrode array using a cyanoacrylate-based glue (similar to Krazy Glue). This method is applicable to both young and aging mice and is suitable for long-term electroencephalographic recordings. In the present experiment, we explored whether the glue-based method is capable of securing individual electrodes in addition to securing the electrode array. C57 black mice aged 25–35 days or 13–19 months were operated on under isoflurane anesthesia. Monopolar or bipolar electrodes were inserted independently in the ipsilateral hippocampal CA3 and entorhinal cortical areas, and they were fixed onto the skull using the glue together with dental acrylic, but without anchoring screws. We found that the implanted electrodes were stable and allowed repeat intracranial recordings and electrical stimulation in freely moving mice.     

A direct test of the unequal-variance signal detection model of recognition memory

Analyses of the receiver operating characteristic (ROC) almost invariably suggest that, on a recognition memory test, the standard deviation of memory strengths associated with the lures (σ_lure) is smaller than that of the targets (σ_target). Often, σ_lure/σ_target ≈ 0.80. However, that conclusion is based on a model that assumes that the memory strength distributions are Gaussian in form. In two experiments, we investigated this issue in a more direct way by asking subjects to simply rate the memory strengths of targets and lures using a 20-point or a 99-point strength scale. The results showed that the standard deviation of the ratings made to the targets (s _target) was, indeed, larger than the standard deviation of the ratings made to the lures (s _lure). Moreover, across subjects, the ratios _lure/s _target correlated highly with the estimate of σ_lure/σtarget obtained from ROC analysis, and both estimates were, on average, approximately equal to 0.80.