Order 1332400: Aphantasia

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Special issue: Research report

The blind mind: No sensory visual imagery in aphantasia

Rebecca Keogh* and Joel Pearson

School of Psychology, University of New South Wales, Sydney, Australia

a r t i c l e i n f o

Article history:

Received 30 January 2017

Reviewed 3 May 2017

Revised 27 June 2017

Accepted 15 October 2017

Published online 28 October 2017

Keywords:

Aphantasia

Visual imagery

Individual differences

Cognition

Mental imagery

* Corresponding author. School of Psycholog E-mail address: [email protected]

https://doi.org/10.1016/j.cortex.2017.10.012 0010-9452/© 2017 Elsevier Ltd. All rights rese

a b s t r a c t

For most people the use of visual imagery is pervasive in daily life, but for a small group of

people the experience of visual imagery is entirely unknown. Research based on subjective

phenomenology indicates that otherwise healthy people can completely lack the experi-

ence of visual imagery, a condition now referred to as aphantasia. As congenital aphan-

tasia has thus far been based on subjective reports, it remains unclear whether individuals

are really unable to imagine visually, or if they have very poor metacognition e they have

images in their mind, but are blind to them. Here we measured sensory imagery in sub-

jectively self-diagnosed aphantasics, using the binocular rivalry paradigm, as well as

measuring their self-rated object and spatial imagery with multiple questionnaires (VVIQ,

SUIS and OSIQ). Unlike, the general population, experimentally naive aphantasics showed

almost no imagery-based rivalry priming. Aphantasic participants' self-rated visual object

imagery was significantly below average, however their spatial imagery scores were above

average. These data suggest that aphantasia is a condition involving a lack of sensory and

phenomenal imagery, and not a lack of metacognition. The possible underlying neuro-

logical cause of aphantasia is discussed as well as future research directions.

© 2017 Elsevier Ltd. All rights reserved.

‘What does a person mean when he closes his eyes or ears

(figuratively speaking) and says, “I see the house where I

was born, the trundle bed in my mother's room where I used to sleep e I can even see my mother as she comes to

tuck me in and I can even hear her voice as she softly says

goodnight”? Touching, of course, but sheer bunk. We are

merely dramatizing. The behaviourist finds no proof in

imagery in all this. We have put these things in words long,

long ago and we constantly rehearse those scenes verbally

whenever the occasion arises’

John B Watson

y, University of New Sou (R. Keogh).

rved.

The study of visual imagery has been a controversial topic

for many years, as the above quote from the behaviourist John

Watson demonstrates. This quote exemplifies the long

running imagery debate of the 1970s and 80's, which centred on the question of whether imagery can be depictive in the format

of its representation (Kosslyn, 2005), or only symbolic or

propositional in nature (Pylyshyn, 2003). However, in the last

few decades psychologists and neuroscientists have made

great strides in showing that visual imagery can be measured

objectively and reliably, and indeed can be depictive/pictorial

in nature, see Pearson and Kosslyn (2015) for a detailed

th Wales, Sydney, Australia.

c o r t e x 1 0 5 ( 2 0 1 8 ) 5 3 e6 054

discussion of the evidence. Research has shown that visual

imagery, like weak perception, impacts subsequent perception

in a myriad of ways (Ishai & Sagi, 1995; Pearson, Clifford, &

Tong, 2008; Winawer, Huk, & Boroditsky, 2010; Zamuner,

Oxner, & Hayward, 2017). For example, the effect of imagery

on subsequent rivalry is specific in orientation and location

space, showing strong evidence for a depictive representation

(Pearson et al., 2008). Imagery has also been shown to activate

early visual cortex and the content of imagery can be decoded

in these areas using an encoding model based on low-level

depictive visual features, such as spatial orientation and

contrast (Naselaris, Olman, Stansbury, Ugurbil, & Gallant,

2015), and recently using features based on a multi-level con-

volutional neural network (Horikawa & Kamitani, 2017).

Additionally, visual imagery has been shown to be closely

related to many cognitive functions such as visual memory

(Albers, Kok, Toni, Dijkerman, & de Lange, 2013; Keogh &

Pearson, 2011, 2014), spatial navigation (Ghaem et al., 1997),

language comprehension (Bergen, Lindsay, Matlock, &

Narayanan, 2007; Zwaan, Stanfield, & Yaxley, 2002), making

moral decisions and making a decision to help others (Amit &

Greene, 2012; Gaesser & Schacter, 2014). Visual imagery also

appears to be elevated (stronger or more vivid) in some psy-

chological and neurological disorders (Matthews, Collins,

Thakkar, & Park, 2014; Sack, van de Ven, Etschenberg,

Schatz, & Linden, 2005; Shine et al., 2015). Visual imagery

has even been employed to assist in cognitive behavioural

therapies such as imaginal exposure and imaginal rescripting

(Arntz, Tiesema, & Kindt, 2007; Holmes, Arntz, & Smucker,

2007; Pearson, Naselaris, Holmes, & Kosslyn, 2015) and the

use of visual imagery during cognitive behavioural therapy

has been shown to be more effective than just verbal pro-

cessing (Pearson et al., 2015).

With strong evidence that visual imagery can be a depictive

cognitive mechanism, the question arises, were Watson,

Pylyshyn and their ilk wrong? Or is it possible that they had a

distinctly different experience of visual imagery that was not

depictive, but more propositional or phonological in nature?

Interestingly, a study investigated exactly this idea and found

that those researchers who were more likely to have been on

the ‘imagery is depictive’ side of the debate tended to report

more vivid imagery, while those who reported weaker imag-

ery were more likely to be on the imagery is propositional side

of the debate (Reisberg, Pearson, & Kosslyn, 2003). One of the

hallmarks of visual imagery is the large range of subjective

reports in the vividness of an individual's imagery. For example, when people are asked to imagine the face of a close

friend or relative some people report imagery so strong it is

almost akin to seeing that person, whereas others report their

imagery as so poor that, although they know they are thinking

about the person, there is no visual image at all. Sir Francis

Galton gave one of the earliest accounts of these subjective

differences in visual imagery in 1883. Galton devised a series

of questionnaires asking participants to imagine a specific

object then describe the ‘illumination’, ‘definition’ and ‘col-

ouring’ of the image. He found, to his surprise, that many of

his fellow scientists professed to experience no visual images

in their mind at all: ‘To my astonishment, I found that the

great majority of the men of science to whom I first applied

protested that mental imagery was unknown to them, and

they, looked on me as fanciful and fantastic in supposing that

the words “mental imagery” really expressed what I believed

everybody supposed them to mean. They had no more notion

of its true nature than a colour-blind man, who has not dis-

cerned his defect, has of the nature of colour. They had a

mental deficiency of which they were unaware, and naturally

enough supposed that those who affirmed they possessed it,

were romancing.” In recent years very little attention has been

given to the ‘poor’ or non-existent side of the visual imagery

spectrum, outside of participants with neurological damage.

Much research during the imagery debate of the 70's and 80's revolved around brain damaged participants who had lost

their ability to imagine, but retained their vision, or vice versa

(Farah, 1988). Recently the idea that some people are wholly

unable to create visual images in mind, without any sort of

neurological damage, psychiatric or psychological disorders,

has seen a resurgence. A recent paper by Zeman, Dewar, and

Della Sala (2015) coined a term for this phenomenon

‘congenital aphantasia’. This study found that these aphan-

tasics all scored very low on the vividness of visual imagery

questionnaire (VVIQ). The VVIQ is a commonly used ques-

tionnaire to measure the subjective vividness of an in-

dividual's visual imagery, by asking them to imagine a friend or relative, as well as scenes and rate the vividness of these

images on a Likert scale. However, a case study reported a 65-

year-old male who became aphantasic after surgery (without

any obvious neurological damage) and was still able to

perform well on other measures of visual imagery, such as

answering questions about the shape of animal's tails. The patient was also able to perform two types of mental rotation

tasks (manikin and ShepardeMetzler tasks), which are

commonly used test of imagery ability (A. Z. Zeman et al.,

2010). Interestingly, his reaction times however, did not

correspond to the rotation distance, which is the common

finding in the literature. These reports suggest the possibility

that aphantasic individuals do actually create images in mind

that they are able to use to solve these tasks, however they are

unaware of these images; that is they lack metacognition, or

an inability to introspect.

Although the visual imagery tasks used in the Zeman et al.

(2010) study are used extensively throughout the imagery

literature, and in clinical settings to measure visual imagery,

the validity of these tasks are somewhat unclear. For example,

in the animal tails test it may be that subjects can use prop-

ositional semantic information about the images they are

asked to imagine, instead of actually creating a visual image in

mind. Additionally, the mental rotation task used (manikin

and ShepardeMetzler tests) could be performed using spatial,

or kinaesthetic imagery, rather than ‘low-level’ visual object

imagery. A relatively new experimental imagery task, which

exploits a visual illusion known as binocular rivalry, allows us

to eliminate many of the issues related to these visual imagery

measures (Pearson, 2014). Binocular rivalry is an illusion, or

process, where one image is presented to the left eye and a

different image to the right, which results in one of the images

becoming dominant while the other is suppressed outside of

awareness (see Fig. 1A for illustration). Previous work has

demonstrated that presenting a very weak visual image of one

of the rivalry patterns prior to the presentation of the binoc-

ular rivalry display, results in a higher probability of that

c o r t e x 1 0 5 ( 2 0 1 8 ) 5 3 e6 0 55

image being seen in the subsequent binocular rivalry pre-

sentation (Brascamp, Knapen, Kanai, van Ee, & van den Berg,

2007; Pearson et al., 2008). Interestingly, when someone

imagines an image instead of being presented with a weak

one, a very similar pattern of results emerges. In other words,

imagery can prime subsequent rivalry dominance much like

weak visual perception (Pearson, 2014; Pearson et al., 2008).

Hence, this imagery paradigm has been referred to as a

measure of the sensory strength of imagery, as it bypasses the

need for any self-reports and directly measures sensory

priming from the mental image.

If an individual is presented with a uniform and passive lu-

minous background while they generate an image, the facilita-

tive effect of their mental image is reduced (Chang, Lewis, &

Pearson, 2013; Keogh & Pearson, 2011, 2014, 2017; Sherwood &

Pearson, 2010). Previous work has shown that these disruptive

effects are limited to visual tasks that require the use of depic-

tive image generation (Keogh & Pearson, 2011, 2014) suggesting

that the early visual areas of the brain are likely involved in the

construction and maintenance of these images. Further, this

priming effect is local in both retinotopic spatial-locations and

orientation feature space (Bergmann, Genç, Kohler, Singer, &

Pearson, 2015; Pearson et al., 2008), further suggesting the

priming is contingent on early visual processes.

This measure of visual imagery also correlates with sub-

jective ratings of visual imagery, both trial-by-trial and ques-

tionnaire ratings, suggesting that participants have insight

into the strength of their own visual imagery (Bergmann et al.,

2015; Rademaker & Pearson, 2012). Here we ran a group of

selfedescribed congenital aphantasics on the binocular ri-

valry visual imagery paradigm to measure the strength of

their sensory imagery. If congenital aphantasia is a complete

lack of visual imagery, we should expect no facilitative prim-

ing effects of visual imagery on subsequent rivalry. However,

if congenital aphantasia is instead a lack of metacognition, or

failed introspection, then we may expect to observe some

priming, despite the subjective reports of no imagery. We

further, tested the aphantasics on a range of standard

Fig. 1 e Binocular rivalry and experimental timeline. A. Illustration o

images are presented, one to each eye, instead of seeing a mix of

Fluctuations only occur for prolonged viewing, not for our brief riv

Participants were cued to imagine one of two images (r ¼ red-hor Participants imagined this image for 6 sec, then after 6 sec they ra

After this they were presented with a very brief binocular rivalry d

questionnaires to probe the vividness and spatial qualities of

their imagery.

1. Methods and materials

1.1. Participants

Fifteen (aged 21e68, 7 female) self-described aphantasic par-

ticipants completed all experiments and questionnaires. The

Aphantasics were recruited through a Facebook page, had

emailed the lab regarding their aphantasia or were referred to

us by Adam Zeman. All aphantasic participants indicated that

they could not remember a time they could imagine and there

was no injury that had led them to becoming aphantasic. We

did not however do a full neurological exam of the partici-

pants. The control, or ‘general population’ group uses data

that was collected over numerous experiments, some of

which were published in a number of different journal articles

(see Keogh & Pearson (2011, 2014); Shine et al. (2015)): while

some are as yet unpublished, all using the same binocular

rivalry visual imagery task, with the exact same stimuli and

instructions, however not all of the studies included vividness

ratings; the sample contains 209 different individuals. The age

range of these 209 participants is from young adult (18 years þ) to elderly (80's). All participants had normal or corrected to normal vision (i.e., wore glasses or contacts).

Fifteen control participants also completed the OSIQ (age

range 18e35, 10 female).

1.2. Stimuli

All participants (in the aphantasic and general population)

were tested in blackened rooms with the lights off, and their

viewing distance from the monitor was 57 cm and was fixed

with the use of a chin rest. The data for the general population

were collected over several years and used several different

computer monitors and testing rooms, as such the stimuli

f an extended binocular rivalry presentation. Two separate

the two, perception alternates between the two images.

alry presentation. B. Binocular rivalry experimental timeline.

izontal Gabor patch and g ¼ green-vertical Gabor patch). ted how vivid the image they created was on a scale of 1e4.

isplay (750 msec) and had to report which colour they saw.

c o r t e x 1 0 5 ( 2 0 1 8 ) 5 3 e6 056

parameters will all be slightly different, due to monitor and

graphics card differences. However, all the experiments were

performed by the same experimenter (RK), who ran all par-

ticipants in the aphantasia and general population studies.

The following specific stimuli parameters described, are for

the aphantasic participants of this study.

In the imagery task the binocular rivalry stimuli consisted

of red horizontal (CIE x ¼ .57, y ¼ .36) and green vertical (CIE x ¼ .28, y ¼ .63) Gabor patterns, 1 cycle/�, Gaussian s ¼ 1.5�. Gabor patterns are sinusoidal gratings with a Gaussian enve-

lope applied. The patterns were presented in an annulus

around the fixation point and both Gabor patterns had a mean

luminance of 4.41 cdm2. The background was black

throughout the entire task during the no luminance condition.

For the imagery luminance condition the background ramped

up to yellow (a mix of the green and red colours used for the

rivalry patterns, with luminance at 4.41 cdm2), during the six-

second imagery period. During this period the background

luminance was smoothly ramped up and down to avoid visual

transients, which may result in attention being directed away

from the task.

Mock rivalry displays were included on 12.5% of trials to

assess any effects of decisional bias in the imagery task. One

half of the mock rivalry stimuli was a red Gabor patch, with

the other half being a green Gabor patch (a spatial mix) and

they shared the same parameters as the green and red Gabor

patches mentioned in the previous paragraph. The mock ri-

valry stimuli were spatially split with blurred edges and the

exact division-path differed on each catch trial (random walk

zigezag edge) to resemble actual piecemeal rivalry. The

aphantasic participants mock priming was not significantly

different to 50% (t(14) ¼ 1.08, p ¼ .30), indicating a lack of decisional priming.

1.3. Experimental procedure

All aphantasic participants came to the University of New

South Wales to participate in approximately 3 h of testing.

They were reimbursed $15 AUD per hour for their participa-

tion in the study. At the beginning of the experimental session

they were briefed verbally about the study (they were told they

were going to fill-in some questionnaires, see some visual il-

lusions, do some memory tests and imagine some pictures)

and written informed consent was obtained. The participants

then completed the following questionnaires and binocular

rivalry task (lasting for about 1e1.5 h) as well as completing

some other memory and imagery tasks for a different study,

not reported on here.

1.4. Questionnaires

All participants completed the vividness of visual imagery

questionnaire (VVIQ2) (Marks, 1973), spontaneous use of im-

agery scale (SUIS) (Reisberg, Culver, Heuer, & Fischman, 1986),

and the object and spatial imagery questionnaire (OSIQ)

(Blajenkova, Kozhevnikov, & Motes, 2006). The VVIQ asks

participants to imagine several scenes and then rate how vivid

their imagery is for each item on a scale of 1e5; with 1 ¼ ‘No image at all, you only “know” that you are thinking of the

object’ and 5 ¼ ‘Perfectly clear and vivid as normal vision’.

Both the SUIS and the OSIQ give participants statements and

they have to rate how much they agree with the statement

from 1 to 5, with 1 ¼ ‘totally disagree’ and 5 ¼ ‘totally agree’. An example question from the SUIS is: ‘When I hear a radio

announcer or DJ I've never actually seen, I usually find myself picturing what they might look like’.

1.5. Binocular rivalry task

Before completing the binocular rivalry imagery task each

participant's eye dominance was assessed (for a more in depth explanation see Pearson et al. (2008)) to ensure rivalry domi-

nance was not being driven by pre-existing eye dominance, as

this would prevent imagery affecting rivalry dominance.

Following the eye dominance task participants completed

either 2 or 3 blocks of 40 trials depending on time constraints

and number of mixed percepts. Mixed percept trials were not

analysed here, so for this reason we attempted to have at least

60 analysable trials per participant, however due to time

constraints and mixes, 4 participants only completed 32, 34,

35, and 45 trials. There was however no correlation between

the number of trials completed and rivalry priming (rs ¼ .04, p ¼ .90, Spearman's correction for non-normality), hence these participants' data are included in the analysis. Participants also completed 2 or 3 blocks of 40 trials of the binocular rivalry

task with a luminous background during the imagery period.

Binocular rivalry imagery paradigm: Fig. 1B shows the time-

line of the binocular rivalry imagery experiment. At the

beginning of each trial participants were presented with

either an ‘R’ or a ‘G’ which cued them to imagine either a red-

horizontal Gabor patch (‘R’) or a green-vertical Gabor patch

(‘G’). Following this, participants were presented with an im-

agery period of 6 sec. In the no luminance condition the

background remained black during this imagery period, in the

luminance condition the background ramped up and down to

yellow over the first and last second of the 6 sec imagery

period to avoid visual transients. After this 6 sec period par-

ticipants were asked to rate how ‘vivid’ the image they

imagined was on a scale of 1e4 (using their left hand on the

numbers on the top of the keyboard) with ‘1’ ¼ ‘No image at all, you only “know” that you are thinking of the object’ and

‘4’ ¼ ‘Perfectly vivid’. After this they were presented with a binocular rivalry display comprising the red-horizontal and

green-vertical Gabor patches and asked to indicate which

image they saw most, of using their right hand on the key pad:

‘1’ ¼ green-vertical, ‘2’ ¼ perfectly mixed, ‘3’ ¼ red-horizontal.

2. Results

Table 1 and Fig. 2AeC show participants' scores on the visual imagery questionnaires. The data supports Zeman et al. (2015)

findings that aphantasic participants rate their imagery as

very poor or non-existent on the VVIQ. These data also show

that participants also rate their spontaneous use of visual

imagery as very low on both the SUIS and Object component

of the OSIQ. Interestingly, the aphantasic participants' spatial component of the OSIQ was almost double that of their object

score. To further assess this finding 15 non-age matched

participants also completed the OSIQ. There was a significant

Table 1 e Average scores on visual imagery questionnaires for the aphantasic participants.

Object OSIQ/75 Spatial OSIQ/75 VVIQ/80 SUIS/60

Total score mean 21.53 41.80 19.00 17.20

Standard deviation 3.46 10.33 6.78 1.65

Fig. 2 e Frequency Histograms for aphantasic participants scores on the VVIQ (Bins ¼ 2) (A), SUIS (Bins ¼ 2) (B) and Object components of the OSIQ (Bins ¼ 2) (C). D. Object and spatial scores on the OSIQ for aphantasic (white bars) and control participants (grey bars). E. Frequency histogram for imagery priming scores for aphantasic participants (yellow bars and

orange line) and general population (grey bars and black dashed line), (Bins ¼ 5). The green dashed line shows chance performance (50% priming). F. Average priming scores for aphantasic participants in the no background luminance

condition (dark grey bar), aphantasic participants in the background luminance condition (white bar) and general

population with no background luminance (light grey bar). G. Mean ‘online’ trial-by-trial vividness ratings for aphantasic

participants in the no background luminance (grey bars) and luminous background condition (white bar). H. Frequency

histogram of Bootstrapping from the general population data (Bins ¼ 1). 15 subjects were randomly chosen, averaged, then returned to the main pool of subjects. Data shows the distribution of the mean of N ¼ 15 for 1000 iterations. The aphantasic mean is shown on the far left (orange dotted line), with a P ¼ .001 chance of pulling such a mean from the general population. All error bars show ±SD's

c o r t e x 1 0 5 ( 2 0 1 8 ) 5 3 e6 0 57

interaction between the spatial and object components of the

OSIQ and the participant group (aphantasic/control), Mixed

repeated measures ANOVA: F(1, 28) ¼ 45.25, p < .001 (see Fig. 2D). Post hoc analysis of the simple effects demonstrated

that as expected the aphantasic participants rated their use of

spontaneous object imagery as significantly lower than the

controls (p < .001). The aphantasics self-rated spontaneous use of spatial imagery was not significantly higher than the

controls (p ¼ .15), mean scores: Aphantasic ¼ 41.80 and control ¼ 36.53.

Next the binocular rivalry imagery priming scores were

examined. As can be seen in Fig. 2E and F, aphantasics had

significantly lower priming on average than our general

sample of participants (ManneWhitney U ¼ 914, p < .01, 2- tailed). In fact, the aphantasic group's priming scores were not significantly different from chance (50%) (Fig. 1E grey filled bar,

one sample t-test: t(14) ¼ .68, p ¼ .51), unlike the general population whose mean is significantly different to chance

(one sample t-test: t(208) ¼ 10.96, p < .001). There were also no correlations between visual imagery priming for the aphan-

tasic participants and any of the questionnaire measures,

likely due to a restriction of range (all p's >. 37). Additionally,

when aphantasic participants completed the task with a lu-

minous background during the imagery period, their priming

was no different to priming in the no luminance condition

(paired sample t-test: t(14) ¼ 1.10 p ¼ .29) and was again not significantly different from chance (one sample t-test:

t(14) ¼ 1.75, p ¼ .10). These results suggest that the aphantasic participant's imagery has little effect on subsequent binocular rivalry. Aphantasic participants' mean ‘online’ trial-by-trial vividness ratings were also very low, with the average rat-

ings not significantly different from the lowest rating of 1 (one

sample t-tests: no luminance condition: t(14) ¼ 1.18, p ¼ .36, luminance condition: 1.37, p ¼ .19, see Fig. 2G). The vividness ratings were not different between the no luminance and

luminance conditions (paired sample t-test: t(14) ¼ 1.10, p ¼ .29).

One possible explanation for the observed differences be-

tween aphantasics and the general population may be that the

eye dominance test simply did not adequately work for the

aphantasic group, thus preventing any imagery priming. If a

participant naturally has one eye that dominates over the

other, this will result in them only seeing the one image that is

presented to that dominant eye e which will result in chance

c o r t e x 1 0 5 ( 2 0 1 8 ) 5 3 e6 058

levels of priming. At the beginning of the imagery experiment

all participants complete an eye dominance task to assess

which eye is dominant. The contrast of the red and green

Gabor patches are then adjusted in accordance with the par-

ticipant's eye dominance, e.g., if the participant sees more green/has a stronger left eye, the contrast of the green Gabor

patch will be decreased, while the red Gabor patch is

increased. This results in each participant having different eye

dominance values. To assess whether eye dominance differ-

ences might be driving our effect, or lack of effect, we

compared eye dominance values (red and green contrasts)

used for the aphantasic participants with 15 other partici-

pants randomly drawn from the general population pool. We

found that there was no significant difference in the eye

dominance values for the aphantasic and control participants,

with no interaction between the contrast values (red/green/

green factor) or group (aphantasic/general population) mixed

repeated measures ANOVA: F(2,56) ¼ .55, p ¼ .58. This suggests that it is unlikely that the aphantasic participants have

different eye dominance compared to the general population,

and it is not driving our observed null effect.

One possible confounding factor is that there may have

been slight variations in stimuli parameters used across

groups due to the general population data being collected

across multiple years on several different computers. To

assess this we looked at a subset of the participants (N ¼ 47) whose data was collected on the same computer in the same

testing room as the aphantasic group. When this was done we

found the same results as when using all 209 participants, that

the aphantasic group priming scores are significantly lower

than the sub-sample from the same room in the general

population: (ManneWhitney U ¼ 200, p ¼ .01). Our aphantasic group sample size was very small

compared to our general population sample (15 vs 209). Hence,

we wanted to ensure our results were not spurious, due to the

small sample size. To further assess this we ran a boot-

strapping resampling analysis to ascertain the probability of

getting the aphantasic mean priming score by randomly

sampling from the general population. To do this we pulled a

random fifteen participants out of our general pool of partic-

ipants and recorded the group mean priming score, this was

done 1000 times, the results of this resampling can be seen in

Fig. 2H. We found that of the 1000 iterations only one had an

average score equal to or less that the mean priming score of

the aphantasic participants, or a probability of p ¼ .001. These results suggest that it is highly unlikely (1 out of a 1000) that

our result is a spurious one due to random chance or our small

sample size.

3. Discussion

Our combined findings from the imagery questionnaires and

psychophysical imagery task support the theory that

congenital aphantasia is characterised by a lack of low-level

sensory visual imagery, and is not due to a lack of metacog-

nition or an inability to introspect. So why is it that some

people appear to be born without visual imagery?

An interesting finding from our results is that while the

aphantasic participants were impaired on all measures of

visual object imagery (lower VVIQ, SUIS, Object OSIQ and

imagery priming scores), they were not impaired on their

spontaneous use of spatial imagery, in fact on average they

rated their spontaneous use of spatial imagery higher than a

control group (although this effect was not significant). This

measure of spatial imagery has been shown to correlate with

performance on mental rotation tasks (Blajenkova et al., 2006).

Interestingly, a case study by Zeman et al. (2010) found that

their patient who developed aphantasia after surgery was still

able to perform perfectly on a mental rotation task. The ‘what’

and ‘where’ pathways of the visual processing stream may

help explain these findings. The dorsal (early visual cortex to

parietal lobes), or ‘where’ stream contains information about

the location of objects in space, while the ventral (early visual

cortex to temporal lobe) or ‘what’ stream contains informa-

tion about an object's identity, which becomes more and more complex as it moves up the hierarchy (Goodale & Milner,

1992). Neuroimaging and brain stimulation work has demon-

strated that mental rotation activates the where pathway

(specifically the parietal cortex) (Harris & Miniussi, 2003;

Jordan, Heinze, Lutz, Kanowski, & Jancke, 2001; Parsons,

2003; Zacks, 2008), in addition to the motor areas such as the

supplementary motor areas and primary motor cortex (Cona,

Marino, & Semenza, 2016; Ganis, Keenan, Kosslyn, & Pascual-

Leone, 2000; Kosslyn, DiGirolamo, Thompson, & Alpert, 1998).

In contrast to this, when participants imagine static images

the visual cortex tends to show increased activity (Cui, Jeter,

Yang, Montague, & Eagleman, 2007; Kosslyn & Thompson,

2003; Kosslyn, Alpert, & Thompson, 1997), although this is

not always the case (D'Esposito et al., 1997; Ishai, Ungerleider, & Haxby, 2000; Mellet et al., 2000), and when individuals

imagine simple Gabor patches the content of the image can be

decoded from early visual cortex (Albers et al., 2013; Koenig-

Robert & Pearson, 2016). Another study has shown that the

level of BOLD response in the visual cortex during an imagery

task correlates with the subjective vividness of an individual's visual imagery (Cui et al., 2007). These results suggest a sep-

aration in the neural networks used in static object imagery

and mental rotation or spatial imagery; as such it may be the

case that aphantasics may have a severe deficiency with the

ventral or ‘what’ pathway, or components of the pathway

such as early visual or temporal cortex, but not the where

pathway.

Research has indicated that when people imagine visual

scenes or objects not just the visual cortex is activated, but

also a large network extending to the parietal and frontal

areas (see Pearson et al. (2015)). It is thought that frontal

engagement is driving feedback connections that activate the

sensory representations in the visual cortex. It may be

possible that aphantasics have a deficit with these feedback

connections from frontal cortex, and are unable to activate

the visual cortex in such a way as to create a visual image in

mind. Recent work from our lab indicates that cortical excit-

ability of both the visual and pre-frontal cortex plays an

important role in governing imagery strength (Keogh,

Bergmann, & Pearson, 2016), hence it may be that aphanta-

sics have abnormal activity levels in either the visual, frontal

or both areas.

Some researchers have suggested that it might be the case

that aphantasic individuals choose not to imagine, as opposed

c o r t e x 1 0 5 ( 2 0 1 8 ) 5 3 e6 0 59

to simply not being able to, possibly due to psychogenic cau-

ses (de Vito & Bartolomeo, 2016), or due to a strong belief that

they cannot imagine, so they do not try. Although the exact

nature of such causes is very difficult to test, we think this is

unlikely for a number of reasons. Firstly, we did not see any

priming or suppression for the included mock-rivalry trials in

the study, which assess possible demand characteristics.

Secondly, participants still reported having spatial imagery in

the OSIQ, which one would not expect if participants were

merely saying they cannot imagine anything. In the OSIQ they

could just respond with 1's for all of the responses, however the low scores were only specific to object imagery questions.

Additionally, many of our participants report that they would

like to be able to imagine visually, and that they have made

attempts to imagine in the past, without success, indicating a

willingness to try to imagine. Some preliminary results from

our lab also indicate that these participants perform above

chance on a mental rotation task, which should not be the

case if these individuals are just refusing to imagine during

any tasks that should involve a visual imagery component.

Future behavioural and neuroimaging results will likely help

to answer this possibility.

Further research should investigate exactly what other

behavioural and cognitive functions are impaired or even

boosted in aphantasics. Additionally, functional neuroimaging

research will be important for identifying possible differences

in regional cortical activity during imagery based tasks as well

as the large scale neuronal networks that may differ in

aphantasics comparedto thegeneralpopulation. Thisresearch

will not only help to improve our understanding of the mech-

anisms of visual imagery, but will help us to understand the

neurological differences that give rise to our vastly different

abilities and experiences of our internal worlds.

Funding

This work was supported by Australian NHMRC grants

GNT1046198 and GNT1085404 and ARC discovery projects

DP140101560 and DP160103299. JP was supported by an

NHMRC Career Development Fellowship GNT1049596.

Acknowledgements

We would like to thank first of all ofour aphantasic participants

who participated in the research. We would also like to give a

special thanks to Adam Zeman for his generous time and

putting us in touch with many of the participants in this study.

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