What your nose really knows: How autism affects your ability to sense social smells

Imagine being able to tell the age, emotional state, and health of a person by a mere sniff....

Well - according to research, this type of subconscious communication is happening all around us!

In fact, many animal species rely on their sense of smell to read emotions and communicate socially, and it is becoming increasingly more evident that humans are using this form of social chemosignaling as well. Human social chemosignals, primarily in the form of sweat (how lovely), is thought to provide information about a wide array of physiological aspects such as; age, disease and emotions - as well as having the ability to influence:

  • Brain activity
  • Hormonal state
  • Mate selection
  • Sexual arousal
  • Infant bonding
  • General psychological and emotional state

So what happens if we are unable to detect these invisible signals?

A recent study published in Nature Neuroscience suggests that individuals with autism spectrum disorder may suffer from distorted chemosignal detection, a term they have coined ‘social dysosmia’. ASD is a developmental disorder characterized by impaired social communication and interaction. Often individuals with ASD will have difficulty interpreting emotional cues, however, the exact reason for this remains unclear. 

Endevelt-Shapira, from the Weizmann Institute of Science, Israel, hypothesized that a portion of the misreading of emotional cues seen in individuals with ASD may be attributed to altered social chemosignaling (or social dysosmia). To investigate this potential link, the study compared the behavioral and autonomic responses of typically developed (TD) and cognitively able adults with ASD to the subliminal presentation of social chemosignals. 

To test this, they conducted a series of different experiments starting with:

  • The handshake experiment - to investigate whether there is a difference between TD and participants with ASD in ‘hand-sniffing’ after shaking someone's hand. (Apparently this is a common way that people subliminally sample other people's body odor!)
  • The Body Odor Discrimination task - to investigate whether there is a difference between the two groups in distinguishing sweat collected from individuals during a sky diving class (containing high levels of cortisol indicative of fear) or sweat from the same person, that had been collected under normal exercising conditions - without feeling fear.

The results of these two experiments showed that everyone likes sniffing their hand after shaking someone else's hand, and it appears that we can all tell the difference between sweat from a fearful skydiver and that from a calm man. Overall there was no difference between the TD and ASD groups, highlighting that individuals with ASD can detect social chemosignals. 

Next up they wanted to explore if there was a difference in autonomic arousal and behavioral responses to the ‘smell of fear’ between TD and ASD groups.

Using electrodermal activity, heart rate, and nasal airflow to measure autonomic arousal 

Twenty TD and twenty ASD male participants were passively exposed to pads soaked with either ‘fear sweat’ or a control (pad only) while performing two cognitive-emotional tasks: the Face Task, where participants are asked to estimate the fearfulness of 27 face images and the well known Stroop task.

Autonomic arousal was primarily measured through electrodermal activity (EDA) using two-finger electrodes connected to an EDA/GSR amplifier. Heart rate and nasal airflow were also measured, using an electrocardiogram (ECG/EKG) and a nasal cannula attached to a spirometer respectively. All signals were recorded using a Power-Lab and analyzed using LabChart 7 software.

Very few participants noticed a change in the odor (3 in each study group), however, the undetected smell of fear resulted in pronounced autonomic arousal in both groups. When TD participants were presented with the smell of fear, their bodies reacted with a classic fear response of increased electrical conductivity in their skin. Surprisingly, the opposite was seen for individuals with ASD - the skydiver sweat lowered their fear response whereas the 'calm' sweat increased it!  

Related: Measuring physiological responses to physical or emotional stimuli

Behavioral responses to the smell of fear

Behavioral responses were measured using a trust-based experiment using manikins which gave hints for a 'spatial location target detection task'. Manikins emitted either a control or fear-smell chemosignal whilst giving participants a spoken hint - which was correct 70% of the time. Interestingly, the results showed that TD individuals trusted the hints given by the control manikin more, whereas the ASD participants trusted the fear-smell manikin more.

Overall the findings of the study showed there was a marked difference in autonomic arousal and behavioral responses to undetected social chemosignals in TD and individuals with ASD. It appears that in individuals with ASD, the problem is not in detecting chemosignals, but rather in the interpretation of them. This gives rise to the condition the researchers have termed social dysosmia, and may be partially attributed to the impaired reading of emotional cues which is characteristic of ASD.

Read more: Predicting emotions from autonomic arousal 



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