A Commentary on:
Phillips and
Silverstein: Convergence of biological
and psychological perspectives on cognitive coordination in schizophrenia. (To appear in BBS 2003)
David Leiser*
Udi Bonshtein
Dept of Behavioral Sciences
Ben-Gurion University
POB 653
IL 84105 Beersheva
Israel
Web
site: www.bgu.ac.il/~dleiser
ABSTRACT
Schizophrenics
exhibit a deficit in theory of mind (ToM), but an intact theory of biology
(ToB). One explanation is that ToM relies on an independent module that is
selectively damaged. Philips and Silverstein analyses suggest an alternative:
ToM requires the type of coordination that is impaired in schizophrenia,
whereas ToB is spared because this type of coordination is not involved.
COMMENTARY
We summarize here work of our own and by
others on the abilities of schizophrenic patients to handle "naïve
theories" in two contrasting domains: Theory of Mind (ToM) and biology
(ToB). ToM is defined as the ability to attribute mental states to the self and
to others, to predict and explain their behavior with reference to mental
states (Premack & Wooduff,
1978). Several recent studies examined ToM in schizophrenia, and all indicate
that ToM is damaged in the acute phase (eg, Frith and Corcoran, 1996; Doody,
Goetz, Johnson, Frith, & Cunnigham-Owens,
1998), but return to normal in periods of remission (Drury, Robinson, &
Birchwood, 1998). This is a specific
deficit that cannot be accounted for by IQ or memory. As is well-know, a
similar specific deficit is found in the case of autism, where it is also
permanent (Baron-Cohen, 1995). The relation between schizophrenia and autism
was pointed out by Frith (1992), who speculated that
there is a common cognitive failing in these two conditions: autists never developed a ToM, whereas schizophrenics
attempt to exercise a lost capability.
One way to test ToM in schizophrenia uses a
non-verbal paradigm, where subjects are presented with cartoons (Sarfati et al. 1997). Each cartoon strip contains three
pictures, which depicts a character performing some activity. Understanding
these strips requires deriving the mental state and goals of the character.
After studying the cartoon strip, subjects are presented with three additional
pictures, one of which provides a suitable ending to the story. One filler
depicts a common everyday activity, performed by the character, while and the
other is very similar to the last picture in the strip. Neither of them is
related to the context of the mental states of the character as established by
the strip. In a variant of the task which involved an absurd
filler (Sarfati et al., 1999) virtually no patients
selected that option. This indicates that the patients do attempt to make sense
of the task, and the paradigm makes it possible to identify the compensatory
strategy used by schizophrenic patients.
Lacking understanding of what the character is up to, schizophrenic
patients who are not disorganized tended to select the picture that is visually
similar to the last picture. Disorganized patients and manic patients tend to
select familiar everyday activities, regardless of its resemblance to the
preceding pictures.
We replicated these findings, and
complemented them with the more common set of stories used to test ToM (Frith & Corcoran, 1996). These stories involve
understanding cheating and false beliefs, either "first-order
beliefs" requiring distinguishing the beliefs of characters from the true
state of affaires, or "second-order beliefs" about others' beliefs.
These stories are read aloud, and simple drawings help the subjects follow and remember
the plots. Schizophrenic performed significantly worse than the control groups
(both normals, and affective disorders hospitalized
patients).
We tested the same subjects for ToB, adapting the battery designed by Johnson and Carey
(1998). This battery relies on two levels of understanding biology, known to
discriminate young from older children. The lower level relies on acquired
information about living beings. The higher level marks accession to the
understanding of living beings as functional systems, which gives meaning to
biological functions. (For instance, since all organisms expand energy, they
all must eat somehow, even if they have no apparent food ingesting organs.) In
their study of Williams Syndrome patients, Johnson and Carey found that for all
their verbal fluency, WS patients remain at the lower, childlike level of
understanding.
Schizophrenic patients test normal on ToB,
even during acute episode. One explanation for this difference between ToM and
ToB would be to posit a "module" or cerebral specialization for ToM (Povinelli & Preuss, 1995). The alternative, "theory-theory"
view, maintains that ToM is acquired like any other naïve theory (Gopnik & Wellman, 1992). On
that view, it would seem difficult to account for the dissociation of ToB and ToM.
We suggest that the challenge of ToM may be
different from that encountered in other naïve theories (Leiser, 2001) The tasks used to test for ToM require coordination of
several pieces of information. Integration of multiple relations is a specific
source of cognitive complexity (Halford et al, 1998;
Waltz et al, 1999, Astington,
Pelletier & Homer, 2002). In the false beliefs tasks, subjects must
hold separate and coordinate the actual state of affairs, the first character's
beliefs about them, and the second's character's beliefs about the first one's.
This coordination is evidently beyond them. In Sarfati’s
paradigm tasks, selecting the right answer implies building a context for his
actions, and this requires coordination of the successive steps. Failing this complex
contextual disambiguation, subjects fall back on either familiar actions to provide meaning, or use a much reduced context,
consisting of the last picture only. If this line of reasoning is correct, we
would have in ToM a symptom that arises, not from a module, but from the
vulnerability of ToM to a deficit in coordination. Preservation of ToB, in
contrast, can be explained by the absence of such coordination once the higher
level of understanding is achieved.
This conclusion remains tentative as an
account of deficits specific to schizophrenia. The authors's
description of the effects of "schizomimetic"
drugs fit psychotic-like state in general, yet non-schizophrenic psychoses (eg affective psychosis) do not damage ToM to the same
extent as schizophrenic psychosis (,Sarfati et al.,
1997; Bonshtein and Leiser, unpublished data).
Equally, Sarfati et al. (1997) reported that a
breakdown of schizophrenia into sub-types is unrelated to the severity of
deficit in ToM, except for disorganized schizophrenia, which is associated with
severe deficit in ToM. But this condition is characterized by a breakdown of
personality and further traits that render cognitive collapse almost
self-evident.
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