Humans report imagining sound where no physical sound is present: we replay conversations, practice speeches, and "hear" music all within the confines of our minds. Research has identified neural substrates underlying auditory imagery; yet deciphering its explicit contents has been elusive. Here we present a novel pupillometric method for decoding what individuals hear "inside their heads". Independent of light, pupils dilate and constrict in response to noradrenergic activity. Hence, stimuli evoking unique and reliable patterns of attention and arousal even when imagined should concurrently produce identifiable patterns of pupil-size dynamics (PSDs). Participants listened to and then silently imagined music while eye-tracked. Using machine learning algorithms, we decoded the imagined songs within- and across-participants following classifier-training on PSDs collected during both imagination and perception. Echoing findings in vision, cross-domain decoding accuracy increased with imagery strength. These data suggest that light-independent PSDs are a neural signature sensitive enough to decode imagination.

Human social behavior relies on the coupling of minds. Here we show that patterns of pupil dilations reveal mental coupling between speakers and listeners. Speakers were videotaped and eye-tracked as they discussed positive and negative autobiographical memories. An independent group of listeners were then eye-tracked while they watched these videos. As pupillary dilations reflect the dynamics of conscious attention, we computed the morphological similarity of speaker-listener pupillary time-series data as a metric of shared attention. The emotional salience of each narrative was also assessed, dynamically, by independent raters. Collective pupillary synchrony between speakers and listeners was greatest during the emotional peaks of a narrative, and decreased as narratives became less engaging. Individual differences in speaker expressivity and listener empathy revealed greatest synchrony in high expressive-high empathic dyads. Together, these findings suggest that pupillary synchrony is an implicit corollary of shared attention that can be used to track mental coupling in real time.

Two sets of items can share the same underlying conceptual structure, while appearing unrelated at a surface level. Humans excel at recognizing and using alignments between such underlying structures in many domains of cognition, most notably in analogical reasoning. Here we show that structural alignment reveals how different people's neural representations of word meaning are preserved across different languages, such that patterns of brain activation can be used to translate words from one language to another. Groups of Chinese and English speakers underwent fMRI scanning while reading words in their respective native languages. Simply by aligning structures representing the two groups' neural semantic spaces, we successfully infer all seven Chinese-English word translations. Beyond language translation, conceptual structural alignment underlies many aspects of high-level cognition, and this work opens the door to deriving many such alignments directly from neural representational content.

The study of human consciousness has historically depended on introspection. However, introspection is constrained by what can be remembered and verbalized. Here, we demonstrate the utility of high temporal resolution pupillometry to track the locus of conscious attention dynamically, over a single trial. While eye-tracked, participants heard several musical clips played diotically (same music in each ear) and, later, dichotically (two clips played simultaneously, one in each ear). During dichotic presentation, participants attended to only one ear. We found that the temporal pattern of pupil dilation dynamics over a single trial discriminated which piece of music was consciously attended on dichotic trials. Deconvolving these pupillary responses further revealed the real-time changes in stimulus salience motivating pupil dilation. Taken together, these results show that pupil dilation patterns during single-exposure to dynamic stimuli can be exploited to discern the contents of conscious attention.

It has long been thought that the eyes index the inner workings of the mind. Consistent with this intuition, empirical research has demonstrated that pupils dilate as a consequence of attentional effort. Recently, Smallwood et al. (2011) demonstrated that pupil dilations not only provide an index of overall attentional effort, but are time-locked to stimulus changes during attention (but not during mind-wandering). This finding suggests that pupil dilations afford a dynamic readout of conscious information processing. However, because stimulus onsets in their study involved shifts in luminance as well as information, they could not determine whether this coupling of stimulus and pupillary dynamics reflected attention to low-level (luminance) or high-level (information) changes. Here, we replicated the methodology and findings of Smallwood et al. (2011) while controlling for luminance changes. When presented with isoluminant digit sequences, participants' pupillary dilations were synchronized with stimulus onsets when attending, but not when mind-wandering. This replicates Smallwood et al. (2011) and clarifies their finding by demonstrating that stimulus-pupil coupling reflects online cognitive processing beyond sensory gain.

Previous research suggests that voting in elections is influenced by appearance-based personality inferences (e.g., whether a political candidate has a competent-looking face). However, since voters cannot objectively evaluate politicians' personality traits, it remains to be seen whether appearance-based inferences about a characteristic continue to influence voting when clear information about that characteristic is available. The authors examine the impact of appearance-based inferences for a characteristic that is well known about candidates: their political affiliation. Across two studies, the authors show that U. S. candidates facing conservative electorates benefit from looking more stereotypically Republican than their rivals (controlling for gender, ethnicity, and age). In contrast, no relationship between political facial stereotypes and voting is found for liberal electorates (using identical controls). The authors further show that this contrast between liberal and conservative electorates has more to do with individual-level differences between liberal and conservative voters than with macro-level differences between liberal and conservative states.

Connecting deeply with another mind is as enigmatic as it is fulfilling. Why people "click'' with some people but not others is one of the great unsolved mysteries of science. However, researchers from psychology and neuroscience are converging on a likely physiological basis for connection - neural synchrony (entrainment). Here, we review research on the necessary precursors for interpersonal synchrony: the ability to detect a mind and resonate with its outputs. Further, We describe potential mechanisms for the development of synchrony between two minds. We then consider recent neuroimaging and behavioral evidence for the adaptive benefits of synchrony, including neural efficiency and the release of a reward signal that promotes future social interaction. In nature, neural synchrony yields behavioral synchrony. Humans use behavioral synchrony to promote neural synchrony, and thus, social bonding. This reverse-engineering of social connection is an important innovation likely underlying this distinctively human capacity to create large-scale social coordination and cohesion.

psychoacoustic theories of dissonance often follow Helmholtz and attribute it to partials (fundamental frequencies or overtones) near enough in frequency to affect the same region of the basilar membrane and therefore to cause roughness, i.e., rapid beating. In contrast, tonal theories attribute dissonance to violations of harmonic principles embodied in Western music. We propose a dual-process theory that embeds roughness within tonal principles. The theory predicts the robust increasing trend in the dissonance of triads: major < minor < diminished < augmented. Previous experiments used too few chords for a comprehensive test of the theory, and so Experiment 1 examined the rated dissonance of all 55 possible three-note chords, and Experiment 2 examined a representative sample of 48 of the possible four-note chords. The participants' ratings concurred reliably and corroborated the dual-process theory. Experiment 3 showed that, as the theory predicts, consonant chords are rated as less dissonant when they occur in a tonal sequence (the cycle of fifths) than in a random sequence, whereas this manipulation has no reliable effect on dissonant chords outside common musical practice.

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We present experimental evidence in support of distributed neural codes for timbre that are implicated in discrimination of musical styles. We used functional magnetic resonance imaging (fMRI) in humans and multivariate pattern analysis (MVPA) to identify activation patterns that encode the perception of rich music audio stimuli from five different musical styles. We show that musical styles can be automatically classified from population codes in bilateral superior temporal sulcus (STS). To investigate the possible link between the acoustic features of the auditory stimuli and neural population codes in STS, we conducted a representational similarity analysis and a multivariate regression-retrieval task. We found that the similarity structure of timbral features of our stimuli resembled the similarity structure of the STS more than any other type of acoustic feature. We also found that a regression model trained on timbral features outperformed models trained on other types of audio features. Our results show that human brain responses to complex, natural music can be differentiated by timbral audio features, emphasizing the importance of timbre in auditory perception.