The main aim of the present study is to investigate whether orally (lingual spray) administered oxytocin influences human social attention and behaviors via oxytocin receptors and whether its effects are dose- and task-dependent.

In a placebo-controlled double-blind between-subject design experiment, investigators plan to investigate whether oral (lingual spray) oxytocin influences human social attention and behaviors via the oxytocin receptor and whether its effects are dose- and task-dependent. Participants complete questionnaires in Chinese versions before treatment administration, including Trait Anxiety Inventory, State Anxiety Inventory, Liebowitz Social Anxiety Scale, Beck Depression Inventory, Autism Spectrum Quotient. Then the first blood (6 ml via indwelling medial cubital vein catheter) and saliva (1-2 ml, passive drool) samples are collected, followed by the first self-administered medication (three sublingual and three supragingival administrations, alternating separated by 30 seconds). After a 15-minute interval, the second medication is administered, with a second blood sample collected immediately afterwards. Participants then remain in the lab for 30 minutes (mobile phone use and conversation with experimenters prohibited during this period). Behavioral experiments commence after the third blood collection. Behavioral experiment consists of four visual attention paradigms including a dynamic task simultaneously contrasting social stimuli (individuals dancing) with geometric patterns; social directed attention using a gaze following paradigm; face emotion processing, and empathy for individuals depicted in natural scenes exhibiting strong positive or negative emotions. During these phases, participants' fixation time, fixation counts and pupil size on specified areas of interest during each visual attention paradigm will be measured using eye tracking equipment. Immediately after completion of the paradigm, participants will complete the state anxiety questionnaire again to assess treatment/paradigm effects on anxiety.

MANOVA tests followed by appropriate post-hoc analyses will be performed on eye-tracking and other data to assess treatment effects. Correlation analysis will be used to assess associations between trait autism scores and outcome measures in the different groups.

Investigators hypothesize that oral oxytocin treatment will dose-dependently facilitate enhanced interest in social stimuli or features in the different visual attention paradigms and dose-dependently increase oxytocin concentrations. Investigators additionally hypothesize that the oxytocin receptor antagonist, atosiban, will reduce interest in social stimuli or features and will prevent facilitatory effects of oxytocin administration but not influence oxytocin concentrations. Investigators hypothesize that oxytocin treatment will increase pupil diameter while viewing some of the social stimuli. Investigators hypothesize that there will be no treatment-dependent effects on state anxiety. Investigators hypothesize that oxytocin effects on enhancing social attention will be greater in individuals with higher scores on trait autism.

Inclusion Criteria:

• Healthy male subjects without past or current psychiatric or neurological disorders

Exclusion Criteria:

• History of or current neurological/psychiatric disorders;
• Use of psychotropic medications (including nicotine)
• Visual impairments

Healthy male subjects without past or current psychiatric or neurological disorders

Participant data will be shared with other qualified researchers upon request