Mental Representations and Unilateral Neglect: A Revealing Clinical Study

June 24, 2015

We are a long way from understanding the complex neural basis for behaviors such as mentalization. But, we can mentally imagine the scientific pursuit of questions, one after another, that might get us to that goal.


An experimental design may be a thing of beauty.

[[{"type":"media","view_mode":"media_crop","fid":"38658","attributes":{"alt":"complex neural basis for behaviors such as mentalization","class":"media-image media-image-right","id":"media_crop_2788164968231","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"3861","media_crop_rotate":"0","media_crop_scale_h":"129","media_crop_scale_w":"150","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"float: right;","title":"© agsandrew/","typeof":"foaf:Image"}}]]In 1978, Edoardo Bisiach and Claudio Luzzatti1 published a study that was both simple and elegant. Their article also taught us something new about the relationship between a person’s perception of the external world and how that same person discerns the world mentally-conjured up in memory, as a “mental representation.”

For psychiatrists, the concept of “mental representation” has great significance because it is a crucial component of theories about empathy, learning, identification, internalization, creativity, self-reflection, and more. For example, the psychological theory of mentalization describes a relational process by which individuals may develop the capacity to form mental representations of the minds of others. According to this theory, mentalization also contributes to an individual’s concept of self. In attempting to grasp the myriad of interacting neurological systems that might underlie a complex, theorized process such as mentalization, it is revealing to look first at a much simpler aspect of mental representation.

In that context, we turn to Bisiach and Luzzatti’s study of mental representation in the visual realm. There were only 2 patients in this study.

I. G. was an 86-year-old woman, a retired manager. N. V. was a male lawyer, aged 72. Both had had right-sided strokes involving the right temporoparietal region. They presented with physical findings that were unremarkable for such a condition and, in addition, both patients had unilateral neglect.

Individuals with unilateral neglect do not respond to stimuli from one side of their environment-generally the left. Normally, we distribute attention to the world around us and locate the source of stimuli, creating a mental map of external space that is body-centric. In unilateral neglect, stimuli that come from the patient’s left side are neglected, whichever way the patient’s body happens to be oriented in space.

Think of a hospitalized patient who is served lunch on a tray. The patient with unilateral neglect, for example, might eat all of the potatoes and broccoli from the right side of his plate but leave the chicken untouched. This would not be because the patient does not like chicken. It would be because the chicken was on the left side of the plate. If a helpful visitor rotated the patient’s plate by 180 degrees, then the patient would eat the chicken because now he would know that it was there.

Unilateral neglect is not a simple sensory deficit. When individuals have a sensory deficit, such as a visual field cut, they naturally compensate by moving their heads to take in all of their surroundings. Unilateral neglect involves all of the sensory realms, although this study only set out to explore the visual modality.

The question that interested Bisiach and Luzzatti was about the mental life of I. G. and that of N. V. Both of these patients had unilateral neglect of the external world, but what of their interior world? To put this another way, even though individuals with unilateral neglect do not notice the left side of their plates in the external world, the question was whether, in their mental world, in the world of their memories, in their mental representations of the external world, they could still conjure up the whole plate? Were they simultaneously aware of potatoes, broccoli, and chicken? How could this question be answered? Here is where Bisiach and Luzzatti’s experimental design-genius is revealed.

Both I. G. and N. V. were familiar with the Piazza del Duomo (in Milan, Italy), which has a prominent cathedral at one end. In the study, the patients were each instructed to first imagine that they were looking at the cathedral from across the piazza. Then they were asked to describe what they could see from this perspective.

I. G. was able to imagine herself looking out at “the cathedral with its steps in front of me.” From this perspective, she reported seeing the Royal Palace and 4 other architectural features. All of the features she mentioned were to her right in the piazza. None were to her left.

How might one explain this? One hypothesis that needed to be ruled out was that perhaps I. G. no longer remembered the buildings that stood to her imagined left in the piazza. Therefore, the researchers asked I. G. to take the opposing perspective-to imagine that she was looking out into the piazza from the doorway of the cathedral. She was then asked to describe what she could see from this vantage point. From this second imaginal perspective, I. G. reported seeing 7 architectural features-streets, arcades, shops. Again, all of these were to her right. In other words, I. G. remembered a total of 11 buildings around the piazza. But even in recollection, in her “mind’s eye,” she only seemed to notice those that were to her right, depending on which way her body was oriented.

The findings from N. V. were similar. Although N. V. mentioned a few features on his left side, the authors noted this about N.V.’s exposition of the parts of remembered scenes: “While central and right-sided items were enumerated in a rather lively manner and sometimes dwelt upon, the few left-sided items were mentioned in a kind of absent-minded, almost annoyed tone.”

These were startling findings! For both I. G. and N. V., unilateral neglect was not confined to perception of the external world. Unilateral neglect extended into the realm of the remembered, the mentally conjured piazza. In other words, there was a deep organization to these individuals’ perceptual and mental experiences.

To expand this idea to other, more familiar realms of behavior, a patient with ADHD does not only misplace his keys and leave drawers open, he is also disorganized in his mental life. Hyperactivity is not simply motor behavior but also a mental state of restlessness.

As another example, individuals with autism spectrum disorder often feel excluded and lonely in their external lives. While they might long for inclusion, many cannot actually conceive of mutuality in relationships. Oliver Sacks2(p259) reported the following about his meeting with Temple Grandin, an accomplished woman with high-level autism: “She was bewildered, she said, by Romeo and Juliet (‘I never knew what they were up to’).” Sacks hypothesizes that this was a consequence of Temple Grandin’s “failure to empathize with the characters, to follow the intricate play of motive and intention.”

Complex behaviors (such as conceptualizing the minds of others) emerge from complex neurological mechanisms that we are only beginning to study. Even seemingly simple behaviors emerge from complex neurological mechanisms, and these are generally out of awareness and unrecognized until something goes awry and someone with a scientific mind decides to investigate.

Edoardo Bisiach and Claudio Luzzatti took one step in a winding scientific pursuit. As with all good science, the Bisiach-Luzzatti paper extended the work of earlier investigators and also opened up new avenues of inquiry. Here are just a few of the questions that this study raised.

Does every patient who exhibits unilateral neglect in the external world also have unilateral neglect that affects his internal mental representations? The answer to this question is no.

And, why would only some individuals have unilateral neglect of both external and internal worlds? Functional MRI studies reveal that damage to frontoparietal circuits within the right hemisphere leads to a disruption in the orienting of attention in external space. Only when there is also damage to fibers that cross the corpus callosum from the frontoparietal circuits does one find disruption of “the symmetrical processing of spatial information from long-term memory.”3

How can one make sense of the fact that some of the architectural features that I. G. and N. V. “saw” in the Piazza del Duomo actually could not have been “seen” from their imagined vantage points because buildings obscured the view?4 This fact raises the question of what I. G. and N. V. were “actually” doing during the study. Were they taking a map perspective? Were they mentally “walking through the piazza?” How much did I. G.’s and N. V.’s reports depend on conceptual knowledge as opposed to mental visualization? This latter possibility raises the question of whether there is such a thing as conceptual neglect.

Even in studying a phenomenon as seemingly simple as the imaginal representation of a remembered external space, it is difficult to separate the contributions of the interacting neural networks involved in spatial navigation from a “helicopter view”; topographical orientation, from a “street view”; conceptual knowledge, mental visualization, distribution of attention, retrieval of various kinds of information, from memory, verbalization of internal mental experiences, and so on.

We are a long way from understanding the complex neural basis for behaviors such as mentalization. But, we can mentally imagine the scientific pursuit of questions, one after another, that might get us to that goal.


Dr Schildkrout is Assistant Clinical Professor of Psychiatry, part-time, at Harvard Medical School, Beth Israel Deaconess Medical Center, in Boston. She is Chair of the Neuropsychiatry Committee of the Group for the Advancement of Psychiatry and author of two books, Unmasking Psychological Symptoms: How Therapists Can Learn to Recognize the Psychological Presentation of Medical Disorders and Masquerading Symptoms: Uncovering Physical Illnesses That Present as Psychological Problems. She reports no conflicts of interest concerning the subject matter of this article.


1. Bisiach E, Luzzatti C. Unilateral neglect of representational space. Cortex. 1978;14:129-133.

2. Sacks O. An Anthropologist on Mars: Seven Paradoxical Tales. New York: Alfred A. Knopf, Inc; 1995.

3. Rode G, Cotton F, Revol P, et al. Representation and disconnection in imaginal neglect. Neuropsychologia. 2010;48:2903-2911.

4. Marshall JC, Halligan PW. Whoever would have imagined it? Bisiach and Luzzatti (1978) on representational neglect in patients IG and NV. In: Code C, Joanette Y, Lecours AR, Wallesch CW, eds. Classic Cases in Neuropsychology. East Sussex, UK: Psychology Press; 2003:257-277.