The fast and the tendinous? Locomotor modifications of the caudal peduncle in Gila spp. from the American Southwest.

In the American Southwest, the fishes within the genus Gila evolved in an environment with seasonal rainstorms that caused stochastic flooding. Some species within this genus, such as bonytail (Gila elegans), possess locomotor morphologies that are similar to those seen in high-performance swimmers such as tuna and lamnid sharks. These shared features include a shallow caudal peduncle, lunate tail, and mechanisms to transmit force from the anterior musculature to the tail fin. We compared the skeletal anatomy of the caudal region of bonytail to roundtail chub (Gila robusta) and humpback chub (Gila cypha) to determine which vertebral elements have been modified to create a shallow peduncle. We also tested the tensile strength of the red (slow oxidative) axial muscle by performing a standard stress test. If the muscle can withstand a large load, this suggests it may play a tendon-like role in transmitting force from the anterior muscle to the hypural plate of the tail. Lastly, we measured the collagen content of the red axial muscle (visualized using serial sections and Masson's trichrome stain) to determine if increased tensile strength is associated with increased collagen content. We found bonytail caudal peduncles are characterized by acute vertebral spines and have red axial muscle that can resist tearing under tension. Roundtail chub peduncles are characterized by relatively more obtuse angles and the red muscle tears easily under tension. Humpback chub possess an intermediate morphology, with relatively obtuse vertebral spine angles and the red muscle can resist tearing under tension. Bonytail have increased collagen content in posterior red axial muscle compared to the anterior musculature also suggesting a tendon-like role of the posterior red muscle. In combination with previous studies of swimming performance, our findings suggest that the axial musculature of bonytail may play a role in transmitting force directly to the shallow peduncle in a manner similar to that of the great lateral tendon of scombrids.

Are Extreme Anatomical Modifications Required for Fish to Move Effectively on Land? Comparative Anatomy of the Posterior Axial Skeleton in the Cyprinodontiformes.

Many teleost fishes with no apparent modifications for life on land are able to produce effective terrestrial locomotor behaviors, including a ballistic behavior called the "tail-flip" jump. Cyprinodontiformes (killifishes, Teleostei: Atherinomorpha) that live at the water's edge vary in morphology and inclination to emerge onto land. Do fish with an amphibious predisposition have extensive modification of the propulsive region of the body when compared to fully aquatic relatives? We quantified body shape and anatomy of the caudal peduncle and tail (the propulsive organ on land and in water) in 11 cyprinodontiform species and two outgroup taxa (Atherinomorpha). We hypothesized that amphibious species would have longer, "shallower" bodies (larger body fineness ratios), deeper (proportionally larger) caudal peduncles, and more robust bones in the tail fin (larger ossified area of the hypural/epural bones) to facilitate locomotor movements on land. We found no evidence of convergence in body shape or skeletal anatomy among species known to make voluntary sojourns onto land. In fact, deep-bodied species, shallow-bodied species, and species with intermediate morphologies all are able to emerge from the water and move on land. It is possible that there are as-yet-undocumented subtle soft-tissue (muscle, tendon, and ligament) modifications that enhance terrestrial locomotor performance in species known to spend large periods of time on land. However, it is also possible that extreme anatomical changes are not required for aquatic cyprinodontiform species to produce effective locomotor movements when they emerge out of the water and move across the land. Anat Rec, 2019. © 2019 American Association for Anatomy.

Revisiting the rise and fall of false recall: presentation rate effects depend on retention interval.

Leading theories of false memory predict that veridical and false recall of lists of semantically associated words can be dissociated by varying the presentation speed during study. Specifically, as presentation rate increases from milliseconds to seconds, veridical recall is predicted to increase monotonically while false recall is predicted to show a rapid rise and then a slow decrease--a pattern shown by McDermott and Watson (2001) in a study using immediate recall tests. In three experiments we tested the generality of the effects of rapid presentation rates on veridical and false memory. In Experiments 1 and 2 participants exhibited high levels of false recall on a delayed recall test, even for very fast stimulus onset asynchronies (SOA)--contrary to predictions from leading theories of false memory. When we switched to an immediate recall test in Experiment 3 we replicated the pattern predicted by the theories and observed by McDermott and Watson. Follow-up analyses further showed that the relative output position of false recalls is not affected by presentation rate, contrary to predictions from fuzzy trace theory. Implications for theories of false memory, including activation monitoring theory and fuzzy trace theory, are discussed.

Does delaying judgments of learning really improve the efficacy of study decisions? Not so much.

A widely held assumption in metamemory is that better, more accurate metamemory monitoring leads to better, more efficacious restudy decisions, reflected in better memory performance--we refer to this causal chain as the restudy selectivity hypothesis. In 3 sets of experiments, we tested this hypothesis by factorially manipulating metamemory monitoring accuracy and self-regulation of study. To manipulate monitoring accuracy, we compared judgments of learning (JOLs) made contemporaneously with a delayed retrieval attempt to JOLs either made at a delay without attempting retrieval or made immediately after study; in previous studies, delayed retrieval-based JOLs have robustly predicted recall with greater relative accuracy than have the other JOL types. To manipulate self-regulation of study, in Experiments 1A-1C and 2A-2C, we compared conditions in which participants' restudy selections were honored with conditions in which they were completely or randomly dishonored; in Experiments 3A-3C, we randomly honored or dishonored half of the restudy selections and half of the nonselections. Results revealed that the benefit of delayed, retrieval-based JOLs for final memory performance was due largely to the selection of more items for restudy rather than to better discriminations between items that would benefit more versus less from restudy. In most cases, gains in recall due to greater self-regulation of study did not increase with better monitoring accuracy; when they did, the effect was extremely small. The surprising conclusion was that restudy decisions were not very much more efficacious under conditions that yield greater monitoring accuracy than under those that do not.

Dynamics of thematic activation in recognition testing.

Two experiments investigated the effects of spreading semantic activation during a recognition test. In Experiment 1, activation spreading during testing from words that were thematic associates of unstudied critical words yielded a linear increase in false alarms to such critical words as the number of tested associates increased, regardless of whether the theme appeared during study or whether any thematic processing occurred during study at all. In Experiment 2, the number of tested associates was held constant, and false alarms to critical words from unstudied themes increased linearly with the strength of association between the critical word and its tested associates, consistent with predictions of spreading-activation theory. For studied themes, however, testing weaker or stronger associates yielded similar rates of such false alarms, contrary to spreading-activation theory. These results suggest that test-induced thematic priming is driven by spreading activation for unstudied themes but by thematic reactivation for studied themes.

Learning from feedback: Spacing and the delay-retention effect.

Most modern research on the effects of feedback during learning has assumed that feedback is an error correction mechanism. Recent studies of feedback-timing effects have suggested that feedback might also strengthen initially correct responses. In an experiment involving cued recall of trivia facts, we directly tested several theories of feedback-timing effects and also examined the effects of restudy and retest trials following immediate and delayed feedback. Results were not consistent with theories assuming that the only function of feedback is to correct initial errors but instead supported a theoretical account assuming that delaying feedback strengthens initially correct responses due to the spacing of encoding opportunities: Delaying feedback increased the probability of correct response perseveration on the final retention test but had minimal effects on error correction or error perseveration probabilities. In a 2nd experiment, the effects of varying the lags between study, test, and feedback trials during learning provided further support for the spacing hypothesis. (PsycINFO Database Record (c) 2009 APA, all rights reserved).

The fSAM model of false recall.

The authors report a new theory of false memory building upon existing associative memory models and implemented in fSAM, the first fully specified quantitative model of false recall. Participants frequently intrude unstudied critical words while recalling lists comprising their strongest semantic associates but infrequently produce other extralist and prior-list intrusions. The authors developed the theory by simulating recall of such lists, using factorial combinations of semantic mechanisms operating at encoding, retrieval, or both stages. During encoding, unstudied words' associations to list context were strengthened in proportion to their strength of semantic association either to each studied word or to all co-rehearsed words. During retrieval, words received preference in proportion to their strength of semantic association to the most recently recalled single word or multiple words. The authors simulated all intrusion types and veridical recall for lists varying in semantic association strength among studied and critical words from the same and different lists. Multiplicative semantic encoding and retrieval mechanisms performed well in combination. Using such combined mechanisms, the authors also simulated several core findings from the Deese-Roediger-McDermott paradigm literature, including developmental patterns, specific list effects, association strength effects, and true-false correlations. These results challenge existing false-memory theories.

Going beyond a single list: modeling the effects of prior experience on episodic free recall.

We present an extension of the search of associative memory (SAM) model that simulates the effects of both prior semantic knowledge and prior episodic experience on episodic free recall. The model incorporates a memory store for preexisting semantic associations, a contextual drift mechanism, a memory search mechanism that uses both episodic and semantic associations, and a large lexicon including both words from prior lists and unpresented words. These features enabled the model to successfully account for the effects of prior semantic knowledge and prior episodic learning on the pattern of correct recalls and intrusions observed in free recall experiments.

Delaying judgments of learning affects memory, not metamemory.

Judgments of learning (JOLs) for cue-target word pairs correlate particularly well with later target recall when made under conditions that permit delayed attempts to retrieve the targets--the delayed-JOL effect. Metamemory theories claim that memory monitoring improves under these conditions. However, another theory--the memory hypothesis--claims that the correlation increases because retrieved items receive a boost in recall from spaced study and are assigned high JOLs, whereas unretrieved items receive no spaced study and, therefore, no boost in recall and, consequently, are assigned low JOLs. When we eliminated differences in spaced study by reexposing word pairs following their JOLs, the delayed-JOL effect disappeared, supporting the memory hypothesis.

Influences of intentional and unintentional forgetting on false memories.

In 2 experiments, we examined the interplay of 2 types of memory errors: forgetting and false memory--errors of omission and commission, respectively. We examined the effects of 2 manipulations known to inhibit retrieval of studied words--directed forgetting and part-list cuing--on the false recall of an unstudied "critical" word following study of its 15 strongest associates. Participants cued to forget the 1st of 2 studied lists before studying the 2nd recalled fewer List 1 words but intruded the missing critical word more often than did participants cued to remember both lists. By contrast, providing some studied words as cues during recall reduced both recall of the remaining studied words and intrusions of the critical word. The results suggest that forgetting can increase or decrease false memories, depending on whether such forgetting reflects impaired access to an entire episode or retrieval competition among elements of an episode.