Traces of Fear in Aphantasia

When reading a vivid story that describes a shark attack, do you imagine yourself in the ocean, seeing the dorsal fin approach you?

“...sun glints off the waves / suddenly a dark flash / in the distant waves / maybe it was a shadow / you turn to the beach / more people are pointing / they look anxious / looking back out to sea / a large fin / slices the surface / moving closer...”

Or is your “mind's eye” — your visual mental imagery of the evocative scene ⁠— essentially a blank?

– early warning: picture of snake below

One's subjective internal life of thinking, perceiving, imagining, and remembering belongs to oneself and nobody else. [Brain scanning is still not a mind reader.] An increasing number of media reports (and scientific studies) have shined a light on this fact: the mental life of one person differs from that of another, sometimes in startling ways. It's always been that way, but now it's out in the open.

The cat is out of the bag.

When reading that sentence, did you have a fleeting mental picture in your mind's eye? Maybe it was clear, maybe it was hazy. Or maybe you saw no visual image at all... if that was the case, you might have a condition known as Aphantasia, the inability to voluntarily generate mental imagery. This is a normal variant of human experience, albeit an uncommon one.

What are the “consequences” of having Aphantasia? You may be more likely to choose a scientific or mathematical occupation, although artists and photographers with Aphantasia certainly exist. Aphantasia is often associated with poor autobiographical memory (diminished ability to recall the past episodes of your life).

Does Aphantasia affect your emotional reactions to ordinary experiences like looking at pictures or reading a story? If visual imagery is important for having an affective response to the shark story, would people with Aphantasia show physiological (bodily) signs of emotion while reading? Wicken and colleagues (2019) asked this question by comparing the skin conductance response (sweaty palms) evoked by reading vs. looking at pictures. This was a pilot study reported in a preprint (not yet peer reviewed).

If visual imagery is necessary for an affective response to evocative stories, then A-Phantasics should have diminished (or absent) skin conductance responses (SCRs) compared to Typical-Phantasics. In contrast, SCRs to unpleasant pictures should not differ between the two groups, because the picture-viewing experience doesn't require imagery. However, it's still possible that imagery-based elaboration (or verbal elaboration, for that matter) could amplify the SCR, especially since each picture was presented for 5 seconds.

For the reading condition, stories were presented as sequential short phrases (to match reading speed across subjects). The control conditions weren't well-matched, unfortunately. This was especially true for Stories, where reading the task instructions served as the neutral comparison condition (instead of reading a neutral story).


Participants

The participants were 24 individuals with intact imagery (based on the Vividness of Visual Imagery Questionnaire and binocular rivalry priming¹ scores within the typical range) and 22 self-identified Aphantasics (who were older, on average, than the control participants).² For the Aphantasia group, seven (out of the original 29) were excluded because their VVIQ or priming scores exceeded the cut-off.


Results

For the Pictures (Perception) condition, the physiological response to Unpleasant vs. Neutral stimuli was not significantly different for the two groups. Incidentally speaking, the skin conductance level (SCL = SCR) was quite variable, as shown in the shaded portion of the graph below.

Adapted from Fig. 1D (Wicken et al., 2019).  Left: Aggregated progressions of baseline-corrected SCL across the duration of the frightening photos sequence (sampled as average across 5 sec time bins). Right: Mean and standard error across time bins.


The Stories were another story... For the Stories (Imagery) condition, the Aphantasic group did not show an elevated SCL for the scary stories, unlike the controls.

Adapted from Fig. 1B (Wicken et al., 2019).


Or as the authors suggested, “[Aphantasia] is associated with a flat-line physiological response to frightening written, but not perceptual scenarios, supporting imagery’s critical role in emotion.”

I'd say “flat-line” is a little judgy, with the semantic implication that the Aphantasics were dead or something.

I'd like to see subjective ratings of emotion (affect and arousal) for the Pictures and Stories, especially since the primary means of identifying people with Aphantasia is based on subjective report. Nonetheless, this is an intriguing finding, with additional evidence forthcoming (or so I imagine)...


Footnotes

¹ See: Is there an objective test for Aphantasia? Binocular rivalry priming can be a useful “objective” measure of aphantasia (Keogh & Pearson, 2018), but it's not necessarily diagnostic at an individual level.

² Mean age = 33.7 yrs for Aphantasia, mean = 23.0 for controls. I don't know why they didn't recruit age-matched controls from the community, other than the convenience of recruiting university students.


Reference

Wicken M, Keogh R, Pearson J. (2019). The critical role of mental imagery in human emotion: insights from Aphantasia. bioRxiv. 2019 Jan 1:726844.

Family fights off shark that bit 16-year-old in North Carolina