Quantifying aphantasia through drawing: Those without visual imagery show deficits in object but not spatial memory

Abstract

Congenital aphantasia is a recently characterized variation of experience defined by the inability to form voluntary visual imagery, in individuals who are otherwise high performing. Because of this specific deficit to visual imagery, individuals with aphantasia serve as an ideal group for probing the nature of representations in visual memory, particularly the interplay of object, spatial, and symbolic information. Here, we conducted a large-scale online study of aphantasia and revealed a dissociation in object and spatial content in their memory representations. Sixty-one individuals with aphantasia and matched controls with typical imagery studied real-world scene images, and were asked to draw them from memory, and then later copy them during a matched perceptual condition. Drawings were objectively quantified by 2,795 online scorers for object and spatial details. Aphantasic participants recalled significantly fewer objects than controls, with less color in their drawings, and an increased reliance on verbal scaffolding. However, aphantasic participants showed high spatial accuracy equivalent to controls, and made significantly fewer memory errors. These differences between groups only manifested during recall, with no differences between groups during the matched perceptual condition. This object-specific memory impairment in individuals with aphantasia provides evidence for separate systems in memory that support object versus spatial information. The study also provides an important experimental validation for the existence of aphantasia as a variation in human imagery experience.

Introduction

Visual imagery, the ability to form visual mental representations of objects or scenes that are not physically in front of us, is a common human cognitive experience, which has been difficult to characterize and quantify. What is the nature of the images that come to mind when forming mental representations of absent items, and are these even visual in nature? What might these representations look like if one lacks visual imagery? Aphantasia is a recently identified variation in experience, defined by an inability to create voluntary visual mental images, although semantic memory and vision is reported to remain intact (Keogh & Pearson, 2018; Zeman, Dewar, & Della Sala, 2015). Aphantasia is still largely uncharacterized, with many of its studies based on case studies or employing small samples of individuals with congenital aphantasia (Brons, 2019; Dawes, Keogh, Andrillon & Pearson, 2020; Jacobs, Schwarzkopf, & Silvanto, 2017; Keogh & Pearson, 2018; Zeman et al., 2015), with few case studies of acquired aphantasia (e.g., Zeman et al., 2010; see also, Botez, Olivier, Vezina, Botez, & Kaufman, 1985). Here, using an online crowd-sourced drawing task designed to quantify the content of visual memories (Bainbridge, Hall, & Baker, 2019), we examine the nature of aphantasics’ mental representations of visual stimuli within a large sample, and reveal differences in behavior for object and spatial imagery.

Although a first study describes individuals with an absence of mental imagery in the 19th century (Galton, 1880), the variation in experience has only recently been defined and named as aphantasia, and there has been very little formal investigation, with only six published studies (Brons, 2019; Dawes, Keogh, Andrillion, & Pearson, 2020; Jacobs et al., 2017; Keogh & Pearson, 2018; Zeman et al., 2015, 2020). This is arguably because most individuals with aphantasia can lead functional, ordinary lives, with many individuals realizing their imagery experience differed from the majority only in adulthood. The current method for identifying if an individual has aphantasia is through subjective self-report, using the Vividness of Visual Imagery Questionnaire (Marks, 1973). However, recent research has begun quantifying the experience using objective measures such as priming during binocular rivalry (Keogh & Pearson, 2018) and skin conductance during reading (Wicken, Keogh, & Pearson, Unpublished results). Since its identification, several prominent figures have come forth describing their experience with aphantasia, including physicist Nicholas Watkins (Watkins, 2018), Firefox co-creator Blake Ross (Ross, 2016), and Ed Catmull, co-founder of Pixar and recently retired president of Walt Disney Animation Studios (Gallagher, 2019), leading to broader recognition of the experience.

Like prosopagnosia (Behrmann & Avidan, 2005), aphantasia is considered to be congenital in the majority of cases, because participants report that they have always experienced a lack of imagery (although it can also be acquired through trauma; Zeman et al., 2010; Thorudottir et al., 2020). A single-participant aphantasia case study found no significant difference from controls in a visual imagery task (judging the location of a target in relation to an imagined shape) nor its matched version of a working memory task, except at the hardest level of difficulty (Jacobs et al., 2017). However, individuals with aphantasia show significantly less imagery-based priming in a binocular rivalry task (Keogh & Pearson, 2018; Pearson, 2019), and show diminished physiological responses to fearful text as compared with controls (Wicken et al., Unpublished results). A recent self-report study has shown that individuals with aphantasia experience less rich autobiographical memories, with some but not all reporting decreased imagery in other sensory domains (Dawes et al., 2020; Zeman et al., 2020). While these studies have observed differences between individuals with aphantasia and controls, the nature of aphantasics’ mental representations during visual recall is still unknown. Understanding these differences in representation between individuals with aphantasia and controls could shed light on broader questions of what information (visual, spatial, symbolic) makes up a memory, and how this information compares to the initial perceptual trace. As individuals with aphantasia are selectively impaired only with imagery but not perception, this suggests perception and imagery do not rely upon identical neural substrates and representations (Dijkstra, Bosch, & van Gerven, 2019). Although this does not exclude the possibility of some overlap in the two processes, this acts as further evidence towards a growing body of work demonstrating key differences between imagery and perception (Bainbridge, Hall, & Baker, 2020; Favila, Lee, & Kuhl, 2020; Lee, Kravitz, & Baker, 2012). Examination into aphantasia thus has wide-reaching potential implications for the understanding of the way we form mental representations of our world.

The nature and content of our visual imagery has proven very difficult to quantify. Several studies in psychology have developed tasks to objectively study the cognitive process of mental imagery through visual working memory or priming (e.g., Marmor & Zaback, 1976; Keogh & Pearson, 2011). The difficulty in objectively quantifying the imagery experience led to a long-standing debate within the imagery literature over the nature of images, and specifically whether visual imagery representations are depictive and picture-like in nature (Kosslyn, 1980, 2005) or symbolic, “propositional” representations (Pylyshyn, 1981, 2003). Neuropsychological research, especially in neuroimaging, has led to large leaps in our understanding of visual imagery. Studies examining the role and activation of the primary visual cortex during imagery tasks have been interpreted as supporting the depictive nature of imagery (Ishai, Ungerleider, & Haxby, 2000; Kosslyn, Ganis, & Thompson, 2001; Schacter et al., 2012; Pearson & Kosslyn, 2015). However, neuropsychological studies have identified patients with dissociable impairments in perception versus imagery (Bartolomeo, 2008; Behrmann, 2000), and recent neuroimaging work has suggested there may be systematically related yet separate cortical areas for perception and imagery, and that the neural representation during imagery may lack much of the richer, elaborative processing of the initial perceptual trace (Lee et al., 2012; Xiao et al., 2017; Silson et al., 2019; Favila, et al., 2020; Bainbridge et al., 2020). Combined with research identifying situations where propositional encoding dominates spatial imagery (e.g., Stevens & Coupe, 1978), researchers have concluded that there is a role for both propositional and depictive elements in the imagery process (e.g., Denis & Cocude, 1989). In their case study, Jacobs et al. (2017) argue that differences in performance between aphantasic participant AI and neurotypical controls may result from different strategies, including a heavier reliance on propositional encoding, relying on a spatial or verbal code. Thus, ideally a task that measures both depictive (visual) and propositional (symbolic) elements of a mental representation could directly compare the strategies used by aphantasic and control participants. In a recent study, impressive levels of both object and spatial detail could be quantified by drawings made by neurotypical adults in a drawing-based visual memory experiment (Bainbridge et al., 2019). The amount of detail included in these memory drawings far surpassed the amount of detail recalled in a matched verbal memory task, suggesting that this drawing task specifically taps into visual mental representations of an item. Such drawings allow a more direct look at the information within one's mental representation of a visual image, in contrast to verbal descriptions or recognition-based tasks. Thus, a drawing task may allow us to identify what fundamental differences exist between individuals with aphantasia and typical imagery, and in turn inform us of what information exists within imagery.

In the current study, we examine the visual memory representations of individuals with congenital aphantasia and typical imagery (controls) for real-world scene images. Through online crowd-sourcing, we leverage the power of the internet to identify and recruit large numbers of both aphantasic (VVIQ ≤ 25) and controls (≥40) for a memory drawing task. We also recruit over 2,700 online scorers to objectively quantify these drawings for object details, spatial details, and errors in the drawings. We discover a selective impairment in aphantasic participants for object memory, with significantly fewer visual details and evidence for increased verbal scaffolding. In contrast, for the items that they remember, aphantasic participants show spatial accuracy at the same high level of precision as controls. Aphantasic participants also show fewer memory errors and memory correction as compared to controls. These results add to a growing body evidence for two separate systems that support object information versus spatial information in memory.