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Brain (1999), 122, 537–559

Memories are made of this: the effects of time on
stored visual knowledge in a case of visual agnosia

M. Jane Riddoch, Glyn W. Humphreys, Theresa Gannon, William Blott and Victoria Jones

School of Psychology, University of Birmingham,
Birmingham, UK

Correspondence to: Professor M. Jane Riddoch,
School of Psychology, University of Birmingham,

BirminghamB15 2TT, UK

Summary

We report the effects of the passage of time on the long-
term visual knowledge for objects in a patient with visual
agnosia (H.J.A.). The naming of real objects was found
to have improved, although this was not associated with
any change in H.J.A.’s basic perceptual abilities which
were stable over a 16-year period. The improvement in
object naming was attributedto better use of non-contour-
based visual information (such as surface detail and depth
cues). In addition, we demonstrate a deterioration in
H.J.A.’s long-term memory for the visual properties of

Keywords: agnosia; stored visual knowledge; visual imagery

objects, and argue that this has occurred as a result of
his having impaired perceptual input. The deterioration
was only apparentin drawing from memory and in the
verbal descriptions of items; with forced-choice testing,
H.J.A. operated at ceiling; we propose that current tests
of visual imagery may not be sufficiently sensitive to
detect subtle impairments of visual memory. Our findings
can be taken to indicate that perceptual and memorial
processes are not functionally independent, but are linked
in an interactivemanner.

Abbreviations: BORB

Birmingham Object Recognition Battery; HF

high frquency; LF

low frequency; SD

structurally dissimilar items; SS

Introduction

structurally similar items

Visual agnosia is a modality-specific disorder where
recognition of visually presented objects is severely
compromised; recognition via other modalities (e.g. touch)
can be relatively unimpaired.The condition was first
described by Lissauer (1890). Lissauer originally
distinguished between two forms of agnosia: apperceptive (a
disorder resulting from impaired perceptual processing) and
associative (a disorder resulting from impaired access to
memory, in the presence of intact perception). More recently,
it has been shown that there are further fractionations within
bothapperceptive and associative forms of agnosia (see
Humphreys and Riddoch, 1987a; Farah, 1990; Humphreys
et al., 1992a). Cases of agnosia typically have been
investigated during the months immediately following the
lesion, and there have been relatively few reports on the
effects of the passage of time on the visual abilities in such
patients (see below). However, the effects of time are ofinterest for at least two reasons: (i) to assess the degree to
which there is spontaneous recovery and/or the development
of compensation strategies; and (ii) to assess what effects
there are on long-term knowledge that was unimpaired at the
time of the original insult. For example, in at least some
cases, long-term visual knowledge appears to be relatively
© Oxford University Press 1999spared even when perceptual processes are severely
compromised (e.g. Riddoch and Humphreys, 1987a;
Behrmann et al., 1992). Is this spared visual knowledge
retained when perceptual input is impoverished?

Effects of time on visual recognition
There are three reports in the literature on the effects of time
in patients with visual agnosia; H.C., initially reported by
Adler (1944, 1950), andthen reassessed 40 years later by
Sparr et al. (1991); J.R., initially reported by Davidoff and
Wilson (1985) and 10 years subsequently by Wilson and
Davidoff (1993); and the case reported by Kertesz (1979),
where there was again a 10 year gap between different
test periods.
H.C.’s initial visual agnosia (for objects, pictures and
faces) was reported to have recovered very quickly. At 6...