Controlled variations in stimulus similarity during learning determine visual discrimination capacity in freely moving mice

The mouse is receiving growing interest as a model organism for studying visual perception. However, little is known about how discrimination and learning interact to produce visual conditioned responses. Here, we adapted a two-alternative forced-choice visual discrimination task for mice and examined how training with equiprobable stimuli of varying similarity influenced conditioned response and discrimination performance as a function of learning. Our results indicate that the slope of the gradients in similarity during training determined the learning rate, the maximum performance and the threshold for successful discrimination. Moreover, the learning process obeyed an inverse relationship between discrimination performance and discriminative resolution, implying that sensitivity within a similarity range cannot be improved without sacrificing performance in another. Our study demonstrates how the interplay between discrimination and learning controls visual discrimination capacity and introduces a new training protocol with quantitative measures to study perceptual learning and visually-guided behavior in freely moving mice

The effect of clinical experience, judgment task difficulty and time pressure on nurses’ confidence calibration in a high fidelity clinical simulation

Background: Misplaced or poorly calibrated confidence in healthcare professionals’ judgments compromises the quality of health care. Using higher fidelity clinical simulations to elicit clinicians’ confidence 'calibration' (i.e. overconfidence or underconfidence) in more realistic settings is a promising but underutilized tactic. In this study we examine nurses’ calibration of confidence with judgment accuracy for critical event risk assessment judgments in a high fidelity simulated clinical environment. The study also explores the effects of clinical experience, task difficulty and time pressure on the relationship between confidence and accuracy. Methods: 63 student and 34 experienced nurses made dichotomous risk assessments on 25 scenarios simulated in a high fidelity clinical environment. Each nurse also assigned a score (0–100) reflecting the level of confidence in their judgments. Scenarios were derived from real patient cases and classified as easy or difficult judgment tasks. Nurses made half of their judgments under time pressure. Confidence calibration statistics were calculated and calibration curves generated. Results: Nurse students were underconfident (mean over/underconfidence score −1.05) and experienced nurses overconfident (mean over/underconfidence score 6.56), P = 0.01. No significant differences in calibration and resolution were found between the two groups (P = 0.80 and P = 0.51, respectively). There was a significant interaction between time pressure and task difficulty on confidence (P = 0.008); time pressure increased confidence in easy cases but reduced confidence in difficult cases. Time pressure had no effect on confidence or accuracy. Judgment task difficulty impacted significantly on nurses’ judgmental accuracy and confidence. A 'hard-easy' effect was observed: nurses were overconfident in difficult judgments and underconfident in easy judgments. Conclusion: Nurses were poorly calibrated when making risk assessment judgments in a high fidelity simulated setting. Nurses with more experience tended toward overconfidence. Whilst time pressure had little effect on calibration, nurses’ over/underconfidence varied significantly with the degree of task difficulty. More research is required to identify strategies to minimize such cognitive biases

Representation of retrieval confidence by single neurons in the human medial temporal lobe

Memory-based decisions are often accompanied by an assessment of choice certainty, but the mechanisms of such confidence judgments remain unknown. We studied the response of 1,065 individual neurons in the human hippocampus and amygdala while neurosurgical patients made memory retrieval decisions together with a confidence judgment. Combining behavioral, neuronal and computational analysis, we identified a population of memory-selective (MS) neurons whose activity signaled stimulus familiarity and confidence, as assessed by subjective report. In contrast, the activity of visually selective (VS) neurons was not sensitive to memory strength. The groups further differed in response latency, tuning and extracellular waveforms. The information provided by MS neurons was sufficient for a race model to decide stimulus familiarity and retrieval confidence. Together, our results indicate a trial-by-trial relationship between a specific group of neurons and declared memory strength in humans. We suggest that VS and MS neurons are a substrate for declarative memories

I Miti dell’Aldilà. Analisi strutturale e interpretazione per una ridefinizione del ruolo del racconto escatologico all’interno del corpus platonico

[cat] Aquest treball té per objecte l'estudi dels tres “mites del més enllà” inclosos en els tres diàlegs de Plató: Gòrgies, Fedó, República. El mateix té com objectiu la redefinició de la funció desenvolupada per les narracions escatològiques dins el corpus platònic, a través d'un estudi de tipus analític dels tres fragments considerats, adreçat a reconstruir -tot i mantenint les especificitats de cadascun dels mateixos i dels diàlegs en els quals s'inclouen - un quadre de conjunt de l'ús, els significats i les finalitats que Plató pretenia atribuïr-los. Aquí, els tres fragments del Gòrgies, del Fedó i de la República no són considerats des de l'únic - per molt evident que sigui - valor ètic i protrètic, però també i especialment, des del punt de vista de les remissions actuades per les imatges de les que estan constituïts respecte de qüestions de notable importància teòrica, desenvolupades dins dels diàlegs als que es refereixen. L'estudi preveu, en la doble via de l'anàlisi estructural i conceptual, que no constitueixen, des de l'òptica d'aquesta investigació, dues vies diferents, sinó dues formes obligatòriament complementàries d'afrontar els “mythoi” considerats. En tot cas, l'estudi es presenta no pas com exclusiu respecte dels fragments específicament analitzats, donat que s'associa al mateix, a efectes de completesa, l'anàlisi conceptual i estructural dels diàlegs dels que formen part, assumint, en un cert sentit, un "caire holístic": els mites escatològics ens recondueixen, de fet, a alguns pilars del pensament platònic, presents no només al Gòrgies, al Fedó i a la República, sinó en el conjunt de la producció filosòfica atenenca. La investigació s'articula en tres parts, una per cada mite considerat: I- El Gòrgies. El mite del judici; II – El Fedó. Els destins de les ànimes; III- La República. La tria. En cada part, hi trobem: un “status quaestionis” que, breument, recapitula els principals filons hermenèutics que s'han desenvolupat al voltant de l'específica narració mítica; l'anàlisi del contingut del fragment, amb un ampli aprofundiment corresponent a les fonts que subministraren a Plató els materials per la construcció de la imatge mítica; l'anàlisi de l'estructura formal dels tres fragments objecte d'anàlisi; la definició dels nuclis i l'estructura conjunta de cada diàleg. Els anàlisi s'alternen regularment amb recapitulacions i reflexions que tenen la finalitat de no deixar que perdem la visió de conjunt que ha de seguir a l'estudi dels detalls. L'anàlisi estructural, que és complementari a la consideració dels nuclis conceptuals, il.lumina la funció dels mites del més enllà que poden ser considerats, de ple dret, part integrant dels diàlegs en els que s'inclouen i "parts serioses" del discurs, ja que es presenten com a narracions capaces d'incloure i sintetitzar, d'un sol cop, els principals nusos teòrics plantejats per cadascun dels diàlegs als que pertanyen oferint, d'aquesta forma, una visió del conjunt de les temàtiques tractades. “Mythos” i “logos”, en el fons, diuen les mateixes coses.[eng] The purpose of the present work is the analysis of the three “myths oft he underworld journey” which are included in Plato’s three dialogues: namely Gorgias, Phaedo and The Republic. The main goal is to re-define the role of eschatological myths within the platonic corpus, through an analytical study of the three passages in which these myths are included, whose aim is to reconstruct a comprehensive framework of their use, meanings and finalities, following Plato’s intents, while keeping the specific features of each passage and of each of the three dialogues in which the passages are included. Here the three passages are not only considered for their unique, even if evident, ethical and protreptic value, but also and above all they look at the recall that images can suggest in respect to important theoretical elements. The study follows the double path of the structural and conceptual analysis which do not constitute two different ways, but rather two complementary ways of dealing with the mythoi. However the present research is not to be thought as exclusively devoted to the analysis of the aforementioned specific passages, since, for completeness, it is correlated to the conceptual and structural analysis of the entire dialogues of which each passage is part of. In this way a “holistic cut” is given: the myths of the underworld journey bring back some of the cornerstones of Plato’s thinking, which are present not only in Gorgias, Phaedo and The Republic, but also in the entire work of the Athenian Philosopher. This work is structured into three main sections, one for each dialogue: I- The Gorgias. The Myth of Judgment; II- The Phaedo. The Fate of Souls; III-The Republic. The Choice. In each part there is: a status quaestionis through which the main hermeneutical key points which are developed around the myth are summarized; the analysis of the content of the passage, with a wide study of the sources that gave Plato the inspiration for the construction of the mythical image; the analysis of the formal structure of the three passages themselves; the definitions of the theoretical cores and of the overall structure of each dialogue. Each analysis is punctually interspersed with recaps and reflections whose purpose is that to keep the global view, this being necessary in order to follow the studies particulars. The structural analysis, which is complementary to that of the conceptual cores, enlightens the role played by the myths of the underworld journey, which can be fully considered integral parts of the dialogues to which they belong and “serious parts” of the speech. Since they are to be seen as narrations capable to encompass and synthesize, at a glance, the principal theoretical issues present in each dialogue, give in this way a full overview of the covered topics. Mythos and logos, after all, say the same things