Encoding Of Changes Research Articles

Finding event structure in time: What recurrent neural networks can tell us about event structure in mind

Under a theory of event representations that defines events as dynamic changes in objects across both time and space, as in the proposal of Intersecting Object Histories (Altmann & Ekves, 2019), the encoding of changes in state is a fundamental first step in building richer representations of events. In other words, there is an inherent dynamic that is captured by our knowledge of events. In the present study, we evaluated the degree to which this dynamic was inferable from just the linguistic signal, without access to visual, sensory, and embodied experience, using recurrent neural networks (RNNs). Recent literature exploring RNNs has largely focused on syntactic and semantic knowledge. We extend this domain of investigation to representations of events within RNNs. In three studies, we find preliminary evidence that RNNs capture, in their internal representations, the extent to which objects change states; for example, that chopping an onion changes the onion by more than just peeling the onion. Moreover, the temporal relationship between state changes is encoded to some extent. We found RNNs are sensitive to how chopping an onion and then weighing it, or first weighing it, entails the onion that is being weighed being in a different state depending on the adverb. Our final study explored what factors influence the propagation of these rudimentary event representations forward into subsequent sentences. We conclude that while there is much still to be learned about the abilities of RNNs (especially in respect of the extent to which they encode objects as specific tokens), we still do not know what are the equivalent representational dynamics in humans. That is, we take the perspective that the exploration of computational models points us to important questions about the nature of the human mind.

Aging and the encoding of changes in events: The role of neural activity pattern reinstatement

When encountering unexpected event changes, memories of relevant past experiences must be updated to form new representations. Current models of memory updating propose that people must first generate memory-based predictions to detect and register that features of the environment have changed, then encode the new event features and integrate them with relevant memories of past experiences to form configural memory representations. Each of these steps may be impaired in older adults. Using functional MRI, we investigated these mechanisms in healthy young and older adults. In the scanner, participants first watched a movie depicting everyday activities in a day of an actor’s life. They next watched a second nearly identical movie in which some scenes ended differently. Crucially, before watching the last part of each activity, the second movie stopped, and participants were asked to mentally replay how the activity previously ended. Three days later, participants were asked to recall the activities. Neural activity pattern reinstatement in medial temporal lobe (MTL) during the replay phase of the second movie was associated with detecting changes and with better memory for the original activity features. Reinstatements in posterior medial cortex (PMC) additionally predicted better memory for changed features. Compared to young adults, older adults showed a reduced ability to detect and remember changes and weaker associations between reinstatement and memory performance. These findings suggest that PMC and MTL contribute to change processing by reinstating previous event features, and that older adults are less able to use reinstatement to update memory for changed features.

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Distinct populations of active cells in the dentate gyrus of the hippocampus may facilitate the unique encoding of changes in the environment.

Control of grip force during restraint of an object held between finger and thumb: responses of muscle and joint afferents from the digits.

Pulling or pushing forces applied to an object gripped between finger and thumb excite tactile afferents in the digits in a manner awarding these afferents probable roles in triggering the reactive increases in grip force and in scaling the changes in grip force to the changes in applied load-force. In the present study we assessed the possible contributions from slowly adapting afferents supplying muscles involved in the generation of grip forces and from digital joint afferents. Impulses were recorded from single afferents via tungsten microelectrodes inserted percutaneously into the median or ulnar nerves of awake human subjects. The subject held a manipulandum with a precision grip between the receptor-related digit (index finger, middle finger, ring finger or thumb) and an opposing digit (thumb or index finger). Ramp-and-hold load forces of various amplitudes (0.5-2.0 N) and ramp rates (2-32 N/s) were delivered tangential to the parallel grip surfaces in both the distal (pulling) and the proximal (pushing) directions. Afferents from the long flexors of the digits (n = 19), regardless of their muscle-spindle or tendon-organ origin, did not respond to the load forces before the onset of the automatic grip response, even with the fastest ramp rates. Their peak discharge closely followed the peak rate of increase in grip force. During the hold phase of the load stimulus, the afferents sustained a tonic discharge. The discharge rates were significantly lower with proximally directed loads despite the mean grip-force being similar in the two directions. This disparity could be explained by the differing contributions of these muscles to the finger-tip forces necessary to restrain the manipulandum in the two directions. Most afferents from the short flexors of the digits (n = 17), including the lumbricals, dorsal interossei, opponens pollicis, and flexor pollicis brevis, did not respond at all, even with the fastest ramps. Furthermore, the ensemble pattern from the joint afferents (n = 6) revealed no significant encoding of changes in finger-tip forces before the onset of the increase in grip force. We conclude that mechanoreceptors in the flexors of the digits and in the interphalangeal joints cannot be awarded a significant role in triggering the automatic changes in grip force. Rather, their responses appeared to reflect the reactive forces generated by the muscles to restrain the object. Hence, it appears that tactile afferents of the skin in contact with the object are the only species of receptor in the hand capable of triggering and initially scaling an appropriate change in grip force in response to an imposed change in load force, but that muscle and joint afferents may provide information related to the reactive forces produced by the subject.

Acoustic features and acoustic change are represented by different central pathways

The central processing of acoustic stimulus changes can be observed neurophysiologically in the mismatch negativity auditory evoked potential (MMN). Stimuli differing in interaural phase were used to investigate the contributions of the primary and non-primary auditory pathways to the encoding of binaural stimuli and to investigate passively elicited measures of binaural processing in experimental animals. In guinea pigs, the MMN was obtained in response to 1000 Hz tones embedded in white noise (S:N = 2 dB). Using a modified oddball paradigm (that is, two stimuli presented in a series, each with a different probability of occurrence), stimuli were presented binaurally with both the tone and noise in-phase to the two ears (S 0N 0) as the standard stimulus and the tone 180° out-of-phase (S ΠN 0) as the deviant stimulus. The MMN, by definition, should occur only in response to a change, or ‘mismatch,’ between the standard and deviant stimuli. The response to the deviant stimulus in the oddball paradigm was compared to the response to the same stimulus when presented in a series alone. The responsesto S 0N 0 and S ΠN 0 collected in a series alone, termed the intrinsic responses, were also compared. Responses were recorded from two surface epidural electrodes — one at the posterior midline and one over the left temporal lobe. AEPs from these locations have been shown to reflect the activity of primary and non-primary thalamo-cortical pathways respectively. A significant MMN was observed at the midline electrode, but no MMN was observed over the temporal lobe. However, there was a significant difference in the intrinsic responses to the two stimuli over the temporal lobe while no difference in the intrinsic responses was seen over the midline. The results suggest that the primary and non-primary auditory pathways appear to provide distinctly different contributions to the encoding of changes in binaural phase. Additionally, the MMN to stimuli differing in interaural phase can be obtained in anesthetized animals and may provide a useful measure of binaural processing.

Differential equation systems for heat‐loss corrections of isoperibolic microcalorimeters: A computer‐modeling approach

AbstractThe problem of adequately correcting thermal titration curves for heat losses in isoperibolic microcalorimeters during rapid reactions in small volumes has been examined. With a data‐acquisition system for the simultaneous encoding of changes in heat, pH, and time linked directly to a DEC‐20 computer, various possible mechanisms for heat‐loss corrections were tested using computer‐modeling techniques. Models expressed by series exponential terms, as commonly used in linear pharmacokinetics to describe the time‐course concentration of a drug, proved to be inadequate to reconstruct the “adiabatic” thermal curve, since its apparent magnitude increased with the time taken for its generation. However, models based on mechanisms incorporating at least two heat sinks, one of which can be equated to the surroundings, have proved successful. The differential equations descriptive of the various models examined have rate constants characteristic of the reaction cell and its inserts, the reaction volume, and the calorimeter used. These can be evaluated by a curve‐fitting algorithm (MLAB) using standard thermal‐titration data (the neutralization of HCL with KOH). Once the rate constants are known, the differential equation solver of MLAB is then used to deconvolute any time: heat‐change matrix to that which would obtain in the absence of heat loss (the “adiabatic” state). With an appropriate differential equation model, the magnitude of the corrected heat change is independent of the time taken for its production and so‐called best model(s) have been judged on the basis of Akaike's information criterion. The application of the heat‐loss correction procedure to the thermal titration of chymotrypsinogen is illustrated.