Humans navigate with stereo olfaction.

Human navigation relies on inputs to our paired eyes and ears. Although we also have two nasal passages, there has been little empirical indication that internostril differences yield directionality in human olfaction without involving the trigeminal system. By using optic flow that captures the pattern of apparent motion of surface elements in a visual scene, we demonstrate through formal psychophysical testing that a moderate binaral concentration disparity of a nontrigeminal odorant consistently biases recipients' perceived direction of self-motion toward the higher-concentration side, despite that they cannot verbalize which nostril smells a stronger odor. We further show that the effect depends on the internostril ratio of odor concentrations and not the numeric difference in concentration between the two nostrils. Taken together, our findings provide behavioral evidence that humans smell in stereo and subconsciously utilize stereo olfactory cues in spatial navigation.

Olfaction spontaneously highlights visual saliency map.

Attention is intrinsic to our perceptual representations of sensory inputs. Best characterized in the visual domain, it is typically depicted as a spotlight moving over a saliency map that topographically encodes strengths of visual features and feedback modulations over the visual scene. By introducing smells to two well-established attentional paradigms, the dot-probe and the visual-search paradigms, we find that a smell reflexively directs attention to the congruent visual image and facilitates visual search of that image without the mediation of visual imagery. Furthermore, such effect is independent of, and can override, top-down bias. We thus propose that smell quality acts as an object feature whose presence enhances the perceptual saliency of that object, thereby guiding the spotlight of visual attention. Our discoveries provide robust empirical evidence for a multimodal saliency map that weighs not only visual but also olfactory inputs.

Mid-Luteal Olfactory Abilities Reveal Healthy Women's Emotional and Cognitive Functions.

Ovarian hormones modulate women's physical and psychological states periodically. Although the olfactory function is increasingly recognized as a reflection of physical and mental health conditions in the clinic, the role of olfaction in emotional and cognitive functions for healthy individuals has yet to be elucidated, especially when taking the menstrual cycle into account. We carried out a comprehensive investigation to explore whether the menstrual cycle could modulate women's olfactory function and whether healthy women's emotional symptoms and behavioral impulsivity could be characterized by their olfactory abilities at a specific menstrual cycle stage. Twenty-nine healthy young women were evaluated repeatedly using a standard olfactory test battery during the late follicular and mid-luteal phases. Their emotional symptoms and behavioral impulsivity were separately quantified via psychometric scales and a stop-signal task. We observed enhanced olfactory discrimination performance during the mid-luteal phase than the late follicular phase. We also found that women's better olfactory discrimination and worse olfactory threshold in the mid-luteal phase predicted fewer individual emotional symptoms and lower behavioral impulsivity, respectively. These relationships were nonetheless absent in the late follicular phase. Our data extend previous clinical observations of the coexistence of olfactory deficits and neuropsychiatric disorders, providing new insights into the significance of olfaction and ovarian hormones for emotional and cognitive functions.

The diagnostic value of the olfactory evaluation for congenital hypogonadotropic hypogonadism.

Objective: The aim of this study was to evaluate the diagnostic accuracy of different olfactory evaluation tools in congenital hypogonadotropic hypogonadism (CHH) patients. Methods: Seventy-one CHH patients were prospectively recruited at Peking Union Medical College Hospital between November 2020 and July 2021. The Chinese Olfactory Function Test (COFT) and Self-reported Olfactory Scale (SROS) were adapted as the subjective tools for the evaluation of olfactory function, and magnetic resonance imaging of olfactory apparatus (MRI-OA) was the objective tool. The olfactory bulb volume (OBV) and the olfactory sulcus depth (OSD) were quantified. Results: Based on the COFT, 36 patients were categorized as having normosmic CHH (nCHH), and the other 35 patients were categorized as having Kallmann syndrome (KS). Among nCHH patients, 35 patients were classified as having normal olfaction and 1 patient had abnormal olfaction by SROS. For KS patients, there were 30 patients grouped into abnormal olfaction, while 5 patients had normal olfaction by SROS. For MRI-OA, 67% (18/27) of nCHH patients showed normal olfactory apparatus, and 33% (9/27) showed bilateral or unilateral olfactory bulb aplasia or hypoplasia. Among KS patients, 96% (27/28) of patients showed bilateral olfactory bulb hypoplasia or aplasia, and 4% (1/28) of patients showed normal olfactory apparatus. All six patients with unilateral olfactory bulb aplasia and three patients with bilateral olfactory bulb aplasia showed normal olfactory function. The accuracy of the SROS in the diagnosis of nCHH and KS was 91.5%, with a sensitivity of 0.857 and a specificity of 0.972, while the accuracy of MRI-OA is 92.7%, with a sensitivity of 0.964 and a specificity of 0.889. Conclusion: SROS and MRI-OA both showed high accuracy to distinguish between KS and nCHH. The abnormal structure of the olfactory apparatus was relatively common in nCHH patients. CHH patients with unilateral olfactory bulb aplasia dysplasia usually had normal olfaction. Normal olfaction without apparent olfactory bulbs is rare but occurred in male CHH patients.

Oxytocin modulates human chemosensory decoding of sex in a dose-dependent manner.

There has been accumulating evidence of human social chemo-signaling, but the underlying mechanisms remain poorly understood. Considering the evolutionarily conserved roles of oxytocin and vasopressin in reproductive and social behaviors, we examined whether the two neuropeptides are involved in the subconscious processing of androsta-4,16,-dien-3-one and estra-1,3,5 (10),16-tetraen-3-ol, two human chemosignals that convey masculinity and femininity to the targeted recipients, respectively. Psychophysical data collected from 216 heterosexual and homosexual men across five experiments totaling 1056 testing sessions consistently showed that such chemosensory communications of masculinity and femininity were blocked by a competitive antagonist of both oxytocin and vasopressin receptors called atosiban, administered nasally. On the other hand, intranasal oxytocin, but not vasopressin, modulated the decoding of androstadienone and estratetraenol in manners that were dose-dependent, nonmonotonic, and contingent upon the recipients' social proficiency. Taken together, these findings establish a causal link between neuroendocrine factors and subconscious chemosensory communications of sex-specific information in humans.

Perception of social interaction compresses subjective duration in an oxytocin-dependent manner.

Communication through body gestures permeates our daily life. Efficient perception of the message therein reflects one's social cognitive competency. Here we report that such competency is manifested temporally as shortened subjective duration of social interactions: motion sequences showing agents acting communicatively are perceived to be significantly shorter in duration as compared with those acting noncommunicatively. The strength of this effect is negatively correlated with one's autistic-like tendency. Critically, intranasal oxytocin administration restores the temporal compression effect in socially less proficient individuals, whereas the administration of atosiban, a competitive antagonist of oxytocin, diminishes the effect in socially proficient individuals. These findings indicate that perceived time, rather than being a faithful representation of physical time, is highly idiosyncratic and ingrained with one's personality trait. Moreover, they suggest that oxytocin is involved in mediating time perception of social interaction, further supporting the role of oxytocin in human social cognition.

Chemosensory communication of gender through two human steroids in a sexually dimorphic manner.

Recent studies have suggested the existence of human sex pheromones, with particular interest in two human steroids: androstadienone (androsta-4,16,-dien-3-one) and estratetraenol (estra-1,3,5(10),16-tetraen-3-ol). The current study takes a critical step to test the qualification of the two steroids as sex pheromones by examining whether they communicate gender information in a sex-specific manner. By using dynamic point-light displays that portray the gaits of walkers whose gender is digitally morphed from male to female [1, 2], we show that smelling androstadienone systematically biases heterosexual females, but not males, toward perceiving the walkers as more masculine. By contrast, smelling estratetraenol systematically biases heterosexual males, but not females, toward perceiving the walkers as more feminine. Homosexual males exhibit a response pattern akin to that of heterosexual females, whereas bisexual or homosexual females fall in between heterosexual males and females. These effects are obtained despite that the olfactory stimuli are not explicitly discriminable. The results provide the first direct evidence that the two human steroids communicate opposite gender information that is differentially effective to the two sex groups based on their sexual orientation. Moreover, they demonstrate that human visual gender perception draws on subconscious chemosensory biological cues, an effect that has been hitherto unsuspected.