When mental images are very detailed: image generation and memory performance as a function of age

Acta Psychologica 113 (2003) 297–314

www.elsevier.com/locate/actpsy

When mental images are very detailed:image generation and memory performance

as a function of age

Paola Palladino a,*, Rossana De Beni b

a Dipartimento di Psicologia, University of Pavia, pizza Botta 6, 27100 Pavia, Italyb Dipartimento di Psicologia Generale, University of Padova, via Venezia 8, 35131 Padova, Italy

Received 24 May 2002; received in revised form 4 February 2003; accepted 6 April 2003

Abstract

Older adults appear to have problems in mental imagery which seem to influence memory,

such as in the recall of concrete words. However, the effects of imagery instruction on old par-

ticipants� memory are quite inconsistent (Richardson, 1980; Salthouse, 1992).

Two experiments explored the effects of aging on the nature of mental images generated

from non-related nouns, and their memory. A sample of 234 participants, young (20–22 years)

young–old (55–65 years), old (66–75 years) and old–old (>75 years), were recruited from uni-

versities and recreation centres. In Experiment 1 participants were required to generate mental

images and describe them accurately in 40 s. Mental images were classified as general, specific-

contextual and self-referred. Details were distinguished between relevant, information useful

for describing a mental image and irrelevant, information which is not pertinent, or useful

for describing a mental image. A final memory task was proposed. In Experiment 2 evocation

and description time was manipulated in order to reduce the production of irrelevant detail: a

shorter condition (evocation+description time¼ 20 s) and a longer condition (evocation+de-

scription time¼ 40 s). Results show that older adults

(1) produce a higher number of general and self-referred images but a lower number of specific

images;

(2) report a greater quantity of irrelevant detail;

(3) recall a lower number of items.

* Corresponding author. Tel.: +39-382-506271; fax: +39-382-506272.

E-mail address: [email protected] (P. Palladino).

0001-6918/03/$ - see front matter � 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0001-6918(03)00045-3

mail to: [email protected]

298 P. Palladino, R. De Beni / Acta Psychologica 113 (2003) 297–314

Decrease in evocation and description time reduced the irrelevant details and increased

older adults� memory performance.

� 2003 Elsevier Science B.V. All rights reserved.

PsycINFO classification: 2340

Keywords: Aging; Imagery; Memory

1. Introduction

Older adults appear to have noticeable difficulty in generating, maintaining and

manipulating mental images (Craik & Dirkx, 1992; Dror & Kosslyn, 1994; for a re-

view see also Salthouse, 1992). Dror and Kosslyn (1994) compared two groups of

young and old participants in four visual mental imagery tasks in each of which a

different imagery process was involved: image generation, image maintenance, imageinspection and image transformation. Significantly, older participants failed in image

activation and image rotation, and also performed poorly in image maintenance.

Craik and Dirkx (1992) also found significant age-related differences in three tests

requiring mental images to be generated and manipulated.

As the helpful role of mental imagery in supporting various cognitive processes is

well known, and also quite a common experience (Richardson, 1980), it is reasonable

to hypothesise that less efficient mental imagery processes could contribute to older

adults performing poorly in many tasks. For example, older adults could be disad-vantaged by mental imagery deficiency in remembering concrete words. The superi-

ority of concrete (high imagery) vs. abstract (low imagery) words in a recall test has

been observed repeatedly and attributed to the higher imagery potential of concrete

words (see for example Paivio, 1971, 1986). Poor imagery processes should reduce

the advantage of concrete words. In fact, older adults have repeatedly shown little

or no advantage in recalling concrete word lists, even after imagery mnemonic in-

struction (Dirkx & Craik, 1992; Isingrini, Fontaine, Metras, Bonneau, & Rey,

1994; Richardson & Rossan, 1994). However, contrasting results have been reportedin the literature (see for example Mason & Smith, 1977; Witte & Freund, 1976) and

many studies have shown that poor memory performances by older adults can be

consistently improved by training in the use of mental imagery (Floyd & Scogin,

1998; Verhaeghen, Marcoen, & Goossens, 1993).

When stimulated towards a more systematic and strategic use of mental imagery,

older adults seem to be aided in memory tasks. However, if untrained, or instructed

in a simple manner, older adults often seem to gain no advantage from the use of men-

tal imagery processes in related memory tasks. Therefore, the relationship between dif-ficulty in mental imagery processing and no consistent advantage for related memory

performances in older adults has not been completely clarified.Dirkx andCraik (1992),

for example, in their second experiment, could not clearly demonstrate a lower involve-

ment of visual imagery in older adults� memory processes for concrete words. In fact,

visual interference was equally disruptive for recall in both young and old age groups.

P. Palladino, R. De Beni / Acta Psychologica 113 (2003) 297–314 299

The difficulty shown by older adults in imagery processes could be interpreted in

terms of age-related general processing deficits. For example, older adults� poorermental imagery processes could be partly due to a deficit in available cognitive re-

sources, as suggested by Craik and Byrd (1982). They hypothesised that older adults

have difficulty in spontaneously using appropriate mnemonic strategies, such as gen-erating a mental image, that place heavy demands on cognitive processing resources.

Another possible account of age-related memory differences involves inhibitory

control. These differences, consistently demonstrated with various tasks and materi-

als (for meta-analyses see Babcock & Salthouse, 1990; Verhaeghen et al., 1993), have

been attributed to poor inhibitory processes that allow irrelevant information to

overload memory. Research examining working memory performance in older

adults shows that they allow irrelevant thoughts to maintain or reach conspicuous

activation, thus interfering significantly in the memory for more relevant materials(see for example, Hartmann & Hasher, 1991; Hasher, Quig, & May, 1997; Hasher

& Zacks, 1988; Palladino & De Beni, 1999). This interpretation could also be ex-

tended to explain age limitations on memory performance as a function of imagery

processing. It can be hypothesised that older adults generate mental images that are

not only qualitatively different from young adults� images but, in particular, are as-

sociated with the generation of irrelevant information. The difficulty in controlling

irrelevant thoughts could interfere with the image generation process, reducing the

benefit that visual coding normally produces in memory.In fact, it has been consistently demonstrated that there are various kinds of men-

tal images. Mental images can be grouped in categories with different properties and

different effects on memory (see for example, Cornoldi, De Beni, & Pra Baldi, 1989;

De Beni & Pazzaglia, 1995; Einstein & McDaniell, 1987). De Beni and Pazzaglia

(1995) collected evidence for the existence of four kinds of mental images: general,

contextual, specific and self-referred images. Contextual, specific and self-referred

image descriptions are richer in detail and more frequently recalled than general im-

ages. Furthermore, the former are sensitive to an increase in generation time. It isreasonable to hypothesise that the type of image a participant prefers to generate,

as well as the associated details, could vary with age. It is also possible to hypothesise

that older adults show poor memory performance associated with problems in image

processing as they also fail to control irrelevant information during generation and

maintenance of mental images in working memory. To verify these hypotheses, two

experiments were conducted in which mental images spontaneously generated from a

list of concrete-high-imagery words were examined. Different age groups were re-

quired to generate and describe mental images and subsequently to recall the wordspresented.

We formulated the hypothesis that memory of mental images differs between

older and younger adults. The specific methodological design adopted here allows

participants to freely generate the type of image they prefer. While it does not allow

a direct test of the relationship between image type and memory, this methodology

offers a more indirect examination of the question whether memory differences could

depend upon the kind of image generated or upon the details associated with each

image, or both. Older adults� mental image descriptions were systematically analysed


to classify image types and to distinguish between image details which increased the

goodness and specification of the image, and those that did not positively contribute

to describing the image, but simply overloaded memory. Although inefficient inhib-

itory mechanisms should not influence the production of relevant details, they could

allow the generation of a greater number of unrelated details.The first experiment was aimed at investigating these aspects for spontaneously

generated images and their memory. A more rigid time constraint was introduced

in the second experiment to control effects due to irrelevant detail.

To control the influence of cohort provenance (Fozard, Metter, & Brant, 1990;

Schaie, 1986), at least partially, the experiments were also conducted with a cross-

sectional design involving adjacent groups of old adults. Participants within an

old age group were assigned to groups of young old and older participants, all of

which were matched for variables related to cohort provenance such as the natureand amount of education.

2. Experiment 1

The goals of this first experiment were to examine the kind and properties of spon-

taneously generated images and associated inhibitory control, and to assess the re-

lated memory performance in different age groups. Mental images were classifiedinto four different categories and details, reported in the image description, were

computed and divided into relevant and irrelevant.

2.1. Method

2.1.1. Participants

Eighty young and old adults agreed to participate in this experiment. Sixty old

adults, 30 men and 30 women, aged from 55 to 88, were recruited from universitiesand recreation centres in the North of Italy. According to reports from a short inter-

view all participants were completely healthy and were not taking any medication

that might have affected their cognitive functioning. All participants were self-suffi-

cient, living independently and were active members of their local community. Old

participants were divided into three groups different for age, and a fourth group

comprised undergraduate students who participated as volunteers in the experiment

to gain credits for a Psychology course:

young 20–22 years old, mean age¼ 21.05 years (20 participants);

young–old 55–65 years old, mean age¼ 61.5 years (20 participants);

old 66–75 years old, mean age¼ 69.1 years (20 participants);

old–old older than 75 years, mean age¼ 79.8 years (20 participants).

Groups were homogeneous for socio-cultural level (Baltes & Baltes, 1990) and

groups of old participants had a comparable number of years education (young–old: M ¼ 10:60, SD¼ 3.53; old: M ¼ 11:25, SD¼ 3.32; old–old: M ¼ 10:85,


SD¼ 3.80). Educational/professional level (Baltes & Baltes, 1990) was comparable

between young and old groups each showing on average a high educational level

(comparable to a secondary school diploma). However the level of education of

young participants was more homogeneous within-group than old participants, as

all were undergraduate students attending first and/or second year courses (13–14years of education).

2.1.2. Materials and procedure

Forty high-imagery value nouns, all having medium–high frequency in Italian,

calculated on the basis of 500,000 (50> use value > 5), were drawn from Cornoldi�srepertoire (1974) and from Bortolini, Tagliavini, and Zampolli (1972).

Participants were tested individually in a quiet room. They were instructed to gen-

erate and describe a mental image for each of the 40 words on the list and to recall asmany words as possible at the end of the list. The experimenter gave simple and ge-

neric information about mental images accompanied by the following instructions:

‘‘If I say the word window you should try to imagine a window in your mind. When

the image is clear and distinct you can start to describe it as you see it’’. For each

word participants had 40 s to generate and describe the image and, at the end of

the list, after about 1 min of conversation with the experimenter, participants were

given an expected free recall task.

The list included the following examples:

calza (sock), torta (cake), palla (ball), forno (oven), borsa (bag), penna (pen), etc.

2.1.2.1. Scoring. Two independent judges classified images generated by participantsinto four main categories according to the literature (Cornoldi et al., 1989; De Beni

& Pazzaglia, 1995):

General images, when participant�s descriptions did not specify any characteristics

or details of the image. For instance, given the noun ‘‘bag’’ (borsa) the description

of a general image could be ‘‘I can see a bag that could contain useful things’’ or

given the noun ‘‘rope’’ (corda) the description of a general image could be ‘‘I can

see a rope that could be used for a tug-of-war’’;

Specific images, when participants reported some characteristics or details of the

image. For instance, ‘‘I can see an empty bag, silver inside and red on the outside,

a little worn underneath’’ or with the word ‘‘cradle’’ (culla) ‘‘I can see an old cra-dle, made of rattan, with a white woollen blanket’’;

Contextual images, when the object was represented with others. For instance, ‘‘I

can see a child with a bag of marbles surrounded by friends in a city park’’;

Self-referred images, when participants report objects in relation to themselves.

For instance, ‘‘I can see the bag they gave me when I went to visit my son in Ec-

uador, with a can of coke inside. My son was happy to see me and my husband’’.

Another example with the word ‘‘cat’’ is ‘‘I can see the black cat I had when I was

child, it was cute with white spots on its back. My father did not want me to havea cat, he preferred dogs’’.


After independent classification, judges compared their rates and debated the dis-

cordant cases in order to reach an agreement.

Details were also computed and divided into

(a) relevant details, information useful for describing a mental image such as

‘‘. . .with a can of coke inside’’ or ‘‘black, cute, with white spots. . .’’, from the ex-

amples of self-referred images;

(b) irrelevant details, information not pertinent or not useful for describing a mental

image such as ‘‘. . .my son was happy to see me and my husband’’ and ‘‘. . .myfather did not want me to have a cat, he preferred dogs’’ from the same exam-

ples.

Irrelevant details were easily distinguishable from relevant. Therefore, after a few

initial comparisons, only one judge continued to classify and compute irrelevant de-

tails.

2.2. Results

As more than one image per word was sometimes produced, a percentage of each

kind of image was computed on the total number of images generated by each par-ticipant. Given that percentages are not independent scores, as the sum must be

100%, a non-parametric test, the Friedman test, was performed. First we contrasted

types of image in each age group. The results show a difference in image type gener-

ated by the young (v ¼ 40:13, p < 0:001), old (v ¼ 14:48, p < 0:01) and old–old

groups (v ¼ 9:35, p < 0:05). A post hoc comparison, with the Wilcoxon matched

pairs signed-ranks test, shows a significant preference for generating specific and

contextual, compared with self-referred and general images, in the young partici-

pants group. By contrast, in the old and old–old groups the preference was for gen-erating general and specific, compared with self-referred (and contextual only in the

group of old–old) images. The groups of old participants were quite homogeneous,

as can be seen in Fig. 1. The group of young–old, although not showing a pattern of

significant differences comparable to the other groups of older participants, showed a

pattern of preference that can be considered a transitional pattern. The types of im-

age generated by young–old group were no longer that observed in young partici-

pants although were not yet that observed in old participants. General images, in

particular, appeared more frequent in the group of young–old than in the groupof young participants although were slightly lower than in old and old–old groups.

Second, we contrasted groups for each type of image with the Kruskal–Wallis

non-parametric test for independent samples. The results show a difference between

groups for general images (v ¼ 22:86, p < 0:001), for self-referred images (v ¼ 22:46,p < 0:001), for contextual images (v ¼ 18:12, p < 0:001), and only approaching sig-

nificance for specific images (v ¼ 6:46, p ¼ 0:09). A post hoc comparison, with the

Mann–Whitney test, again shows a common pattern between old groups (see Fig.

1). Old participants, independently of the specific age group, generated self-referredand general images more frequently than young participants, but generated specific

0

10

20

30

40

50

60

70

gene

ral

spec

ific

cont

extu

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self-

refe

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young

young -old

old

old-old

Fig. 1. Percentages of each type of mental image spontaneously generated by the four age groups.


and contextual images less frequently than young participants, although the differ-

ence in specific image generation was fully significant only between old–old and

young participants.We also distinguished between relevant and irrelevant details reported in the image

description. A relevant detail is information useful for describing a mental image,

whilst irrelevant is information which is neither pertinent nor useful.

Differences between age groups were observed for both the number of rele-

vant (F ð3; 76Þ ¼ 7:64, MSE¼ 1731.59, p < 0:001) and irrelevant details (F ð3; 76Þ ¼11:74, MSE¼ 313.58, p < 0:001) (see Table 1).

Post hoc comparisons with Tukey�s method showed that young–old and old (but

not old–old) participants produced a lower number of relevant details than youngparticipants, whilst old–old and old participants produced a higher number of irrel-

evant details than young participants, p < 0:05.No significant difference between groups of old participants was observed for

number of relevant details indicating that they were quite homogeneous. How-

ever only the group of old–old adults did not differ significantly from the group of

younger participants.

The comparison between old–old and young participants shows that although

they did not differ in number of relevant details old–old participants produced moreirrelevant details.

An analysis of final recall shows a main effect of age group (F ð3; 76Þ ¼ 12:44,MSE¼ 15.41, p < 0:01). Post hoc comparisons with Tukey�s method show

that old–old and old participants had a poorer memory performance than young

Table 1

Number of relevant and irrelevant details per age group

Young Young–old Old Old–old

Relevant details 213.40 (46.12) 159.40 (31.73) 159.25 (31.56) 184.20 (52.88)

Irrelevant details 0.30 (0.92) 11.95 (10.36) 25 (22.06) 30.55 (25.68)


participants, M ¼ 13:5 (SD¼ 14.73), M ¼ 16:15 (SD¼ 3.47) and M ¼ 20:5 (SD¼3.93) respectively, and old–old even poorer than young old, M ¼ 18:95 (SD¼3.44), p < 0:05.

2.3. Discussion

Age-related differences were observed for both the kind of image spontaneously

generated and the number of relevant and irrelevant details reported in the image de-

scriptions.

Old–old participants produced proportionally more general and self-referred

kinds of image than young participants. Furthermore, the type of image more fre-

quently generated in each of these two age groups was different. Young participants

spontaneously generated more specific and contextual images whilst old–old partic-ipants generated a higher number of general and specific images, although the latter

were significantly less frequent than for young participants (see Fig. 1).

Younger groups of old participants did not show a significant preference for a

type of image although their frequency generation profiles mirrored the profiles of

old–old participants. In fact, the young–old generated a higher number of general

and self-referred images and a lower number of contextual images compared with

young participants. Therefore, it seems that young–old participants show tendencies

that consolidate with aging, suggesting that this age range could reflect a transitionperiod. It must also be noted that no significant difference in type of image generated

was observed between the groups of old adults. We can therefore conclude that pref-

erence for a type of image in a task of spontaneous image generation is quite stable in

later life although differences with young (20–22 years) participants were strongest in

the group older than 75 years.

Age-related differences were also observed for the number of details associated

with images. Old–old participants produced a higher number of irrelevant details al-

though their image descriptions were not less specified than young participants� de-scriptions. Old–old participants� images were comparable to young participants�images for number of relevant details. However their final recall was poorer than

young adults.

Poorer old–old final recall could then be related to both the higher frequency of

general images, which are less memorable (Cornoldi et al., 1989; De Beni & Pazza-

glia, 1995), and to the greater quantity of irrelevant detail that appeared in image

descriptions. In fact, it must be noted that old–old and young participants did not

differ in the images specification, computed as the amount of relevant detail, butin both type of image and the amount of irrelevant detail. According to this obser-

vation we can hypothesise that both image type and quantity of irrelevant detail

could lead to age-related differences in memory performance. Furthermore, we can

also hypothesise that these two variables are related, as it is possible that the gener-

ation of a certain type of image induces a greater production of irrelevant detail.

However, this does not seem to be the case as old–old and young–old participants

generated comparable percentages of each type of image but produced a different

amount of irrelevant detail.


Therefore, according to the results obtained, we can suggest that older adults� dif-ficulty in taking advantage of imagery coding to remember concrete words does not

seem to be due to difficulty in generating highly detailed images but rather could be

related to at least two apparently independent factors: the type of image more fre-

quently generated and the number of irrelevant details that could induce memory in-terference.

3. Experiment 2

In this second experiment we manipulated the opportunity to generate irrelevant

details in order to evaluate the relationship with poor final memory performance. We

presented the same task as in Experiment 1 to different age groups of participants,but in two conditions, with 20 and 40 s for each word. We believe that a reduction

in time available to generate and describe images could reduce the opportunity to

generate irrelevant thoughts. In fact, from an analysis of old–old participants� image

descriptions we noted that irrelevant thoughts typically emerged after an initial ap-

propriate and coherent image description. Hence, time constraints should induce old

participants to give adequate image descriptions and to eliminate excess time that

could allow the intrusion of irrelevant thoughts. We hypothesised that irrelevant

thoughts could be responsible for poor memory performance. Hence a time reduc-tion, decreasing irrelevant thoughts, should improve final recall. According to the re-

sults of Cornoldi et al. (1989) and De Beni and Pazzaglia (1995), we also expected

that the image type generated could be sensitive to time constraints, although partic-

ipants should still be able to generate different types of image, even with the faster

rate proposed (20 s per word).

3.1. Method

3.1.1. Participants

One hundred and twenty participants were involved in this experiment. They had

similar characteristics to participants in Experiment 1. However, as there was no rel-

evant difference between adjacent groups of old adults, we decided to divide the

group of old participants into two groups only: old, aged between 60 and 70 years

(mean age¼ 62.9), and old–old, older than 70 years (mean age¼ 75.2). Each group

comprised 20 participants (10 men and 10 women) and three groups were recruited

for each experimental condition––with 20 and 40 s. Groups were homogeneous forsocio-cultural and educational/professional level (Baltes & Baltes, 1990), each group

showing on average a high educational/professional level.

3.1.2. Material and procedure

The same list was presented in both conditions, 20 and 40 s, to two different

groups of participants. The list comprised 15 of the original 40 words presented in

Experiment 1. The procedure followed Experiment 1, except that participants were


invited to generate and describe only one image per word in order to reduce within-

participant variance.

3.2. Results

Scoring and image classification followed in Experiment 1. As there were very few

contextual images, they were re-classified in the category of specific images.

An analysis of variance 3 · 2 · 3 with Type of image as within-subject factor, with

three levels (general, specific and self-referred), and age and condition as between-

subject factors, with three levels (young, old and old–old) and two levels (20 and

40 s) respectively, was conducted on the number of images generated. A main effect

02468

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spec

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self-

refe

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20sec

40sec

02468

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gene

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spec

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self-

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20sec

40sec

02468

1012

gene

ral

spec

ific

self-r

efer

red

20sec

40sec

(a) young

(b) old

(c) old_old

Fig. 2. Number of generated images of each type by (a) young participants, (b) old participants and

(c) old–old participants.


of type of image was found (F ð2; 228Þ ¼ 90:39, MSE¼ 8.80, p < 0:001). The effect

was due to a higher number of specific vs. general images and more general than

self-referred images (post hoc comparisons with Tukey�s method, p < 0:05). A signif-

icant interaction type of image · condition· age was obtained (F ð4; 228Þ ¼ 5:98,MSE¼ 8.803, p < 0:001). As can be seen in Fig. 2a–c, interaction was due to the factthat young participants did not differ between conditions whilst old and old–old par-

ticipants did. Young participants generated more specific than general and self-

referred images in both conditions (post hoc comparisons with Tukey�s method,

p < 0:05). By contrast, old and old–old participants produced less general images

when more time was available (40 s condition) and produced more self-referred im-

ages, although for old–old participants this difference did not reach significance (post

hoc comparisons with Tukey�s method, p < 0:05). In fact, with 20 s to generate each

image, both groups produced a comparable number of specific and general images,both more frequent than self-referred images. However, with more time available,

they produced a comparable number of specific and self-referred images, both signif-

icantly more frequent than general images (post hoc comparisons with Tukey�smethod, p < 0:05). A reduction in time available induced a significant decrease in

number of general images but an increase in number of self-referred images in both

groups (post hoc comparisons with Tukey�s method, p < 0:05).Two analyses of variance with mixed design, group · condition, were conducted

on the quantity of both (a) relevant and (b) irrelevant details.(a) A main effect of condition (F ð1; 114Þ ¼ 37:11, MSE¼ 90.55, p < 0:001) was

due to the production of a higher number of relevant details with slower generation

rhythm and a main effect of group (F ð2; 114Þ ¼ 6:53, MSE¼ 90.55, p < 0:01) wasdue to the more specified images of younger participants. A significant interaction

condition · age (F ð2; 114Þ ¼ 9:02, MSE¼ 90.55, p < 0:001) showed that young par-

ticipants did not produce more relevant details with increased time (20 s condition:

M ¼ 38:8, SD¼ 8.41; 40 s condition: M ¼ 39:1, SD¼ 10.6), whilst a significant in-

crease in relevant details was observed for old and old–old adults (old, 20 s condi-tion: M ¼ 24:3, SD¼ 10.63; 40 s condition: M ¼ 41:55, SD¼ 7.98; old–old, 20 s

condition: M ¼ 24:70, SD¼ 11.45; 40 s condition: M ¼ 38:9, SD¼ 8.66) (post hoc

comparisons with Tukey�s method, p < 0:05). In the 40 s condition, the three groups

produced a comparable number of relevant details whereas in the 20 s condition

younger participants produced a greater number of relevant details than both groups

of older participants.

(b) A main effect of condition (F ð1; 114Þ ¼ 85:56, MSE¼ 11.86, p < 0:001) wasdue to the production of a higher number of irrelevant details with slower generationrhythm and a main effect of Group (F ð2; 114Þ ¼ 46:93, MSE¼ 11.86, p < 0:001) wasdue to the greater production of irrelevant detail by both groups of older partici-

pants. A significant interaction condition · age (F ð2; 114Þ ¼ 29:02, MSE¼ 11.86,

p < 0:001) showed that young participants did not produce more irrelevant detail

with increased time (20 s condition: M ¼ 1:45, SD¼ 1.95; 40 s condition:

M ¼ 0:80, SD¼ 1.01), whilst a significant increase was observed for old and old–

old adults (old, 20 s condition: M ¼ 2:40, SD¼ 2.96; 40 s condition: M ¼ 13:20,SD¼ 5.55; old–old, 20 s condition: M ¼ 3:70, SD¼ 2.95; 40 s condition: M ¼ 11,


SD¼ 4.25) (post hoc comparisons with Tukey�s method, p < 0:05). In the 40 s con-

dition, both groups of old participants produced significantly more irrelevant detail

than young participants (post hoc comparisons with Tukey�s method, p < 0:05).The test of memory recall showed a main effect of condition due to a generally

higher recall when only 20 s were available. A condition · age interaction ap-proached significance (F ð2; 114Þ ¼ 2:70, MSE¼ 2.60, p ¼ 0:072). Post hoc compari-

sons with Tukey�s method showed that old–old participants recalled less items than

young but, surprisingly, only when they had more time to generate and describe im-

ages, p < 0:05 (see Fig. 3). It must be noted that in this condition (40 s) old–old par-

ticipants produced a significantly higher number of irrelevant details.

Although the condition with slower word presentation favoured the generation of

more detailed and qualitatively more memorable images, it is surprising that old–old

adults performed worse than for words presented at a faster rate. Although an expla-nation could be that old–old participants in this condition produced more irrelevant

details, we wanted to control the potential effect of a time delay between the begin-

ning and the end of presentation. It is possible that older adults are hampered by the

slow rate of presentation because it creates a longer delay between the beginning of

the presentation and the final recall. If the poorer performance of old–old partici-

pants is due to this delay, their recall of the first, and hence more distant, words

should be worse in the 40 s condition. A mixed design ANOVA with Position (first,

central and last words of the list) as within-subject factor and condition (20 vs. 40 s)as between-subject factor, was conducted on words recalled by old–old participants.

A main effect of position (F ð2; 76Þ ¼ 17:62, MSE¼ 1.14, p < 0:001) and a main effect

of condition (F ð1; 38Þ ¼ 12:09, MSE¼ 0.75, p < 0:01) were obtained. Interaction

was far from significant, F < 1. Last words presented were recalled better than first

and centrally positioned words in both conditions (20 s condition: first items

M ¼ 2:05, SD¼ 1.09; intermediate items M ¼ 2:00, SD¼ 1.12; last items M ¼ 3:1,SD¼ 0.85; 40 s condition: first items M ¼ 1:25, SD¼ 0.91, intermediate items

M ¼ 1:5, SD¼ 0.88; last items M ¼ 2:75, SD¼ 1.12) and old–old participants re-called better in the 20 s than in the 40 s condition. Post hoc comparisons with

Tukey�s method showed that recall of first and intermediate items was no different

02468

1012

youn

g old

old-o

ld

20sec

40sec

Fig. 3. Total number of words recalled by the three age groups.


even between conditions, p < 0:05. However we should consider that intermediate

items of the 20 s condition were recalled 100 s after presentation (after five final

words, each presented for 20 s) whereas first items in the 40 s condition were recalled

400 s after presentation (after 10 words, five intermediate and five final, each pre-

sented for 40 s). Therefore a difference of 300 s in delay between first items in the40 s condition and intermediate items in the 20 s condition did not make a difference

in item memorability for old–old participants. Old–old adults� different recall perfor-mance in the two conditions, with 20 and 40 s per word, are not due to a difference in

delay between item presentation and recall between conditions.

3.3. Discussion

As effective changes in age ranges of old participant groups and image classifica-tion were introduced in Experiment 2, a direct comparison between Experiments 1

and 2 is not possible. However the general comparison between young and old adults

shows that the results of Experiment 2 replicate those of the previous experiment. In

fact in the 40 s condition, similar to the previous experiment, age-related differences

were found for type of image, irrelevant detail and memory performance: old adults

prefer to generate self-referred images, introduce more irrelevant details into the im-

age description, and are poorer in final recall. Again, type of image and irrelevant de-

tails appear to be independent. For example, in the 20 s condition, young and olderparticipants did not differ in number of irrelevant details though young participants

generated a higher number of general and specific images than older participants.

Time played a significant role for older participants. Whilst the performance of

young participants was entirely comparable for the 20 and 40 s conditions, given less

time, old and old–old participants generated less self-referred images and produced

less relevant and irrelevant details. The effect of time constraints on the generation of

self-referred images is coherent with results obtained by Cornoldi et al. (1989), who

demonstrated that this kind of image is sensitive to time constraints, and with datacollected by Treat and Reese (1976) showing that older adults� image generation per-

formance is sensitive to time constraints.

In line with our hypotheses, our results also show that time constraints have a

positive effect on the number of irrelevant details. These numbers were significantly

reduced with the faster rate of word presentation. A short time available to generate

and describe mental images may have focused older adults� mental processes on the

task, thus reducing interference.

Exploring memory performance sensitivity to time constraints, the opposite pat-tern of results could be expected regarding the quality and specification of images

and irrelevant details. Time constraints influenced the quality and specification of

images for old adults, leading to a reduction in the number of relevant details and

specific and self-referred images, and a decrease in the number of irrelevant details.

Therefore, if image memorability is mainly influenced by quality of the image gener-

ated and quantity of relevant detail, the memory performance of old participants

should decrease with time constraints. On the contrary, if image memorability is

mainly disturbed by irrelevant detail, a time reduction should benefit the memory


performance of old participants. A third possibility could be that, as changes related

to time constraints go in the opposite direction, the sum of positive and negative ef-

fects should not produce any effect on memory performance.

Results show that old–old participants� final recall improved in the shorter presen-

tation rate condition suggesting that their memory performance was mainly affectedby better control of intrusive thoughts.

These results are in line with the inhibition hypothesis (Hasher & Zacks, 1988). In

fact, the interference produced by irrelevant details appears to damage the memory

performance of older participants. Moreover, in the slower presentation rate condi-

tion, older participants appear not to benefit from either the increased generation of

more memorable image types or the greater quantity of relevant detail. Furthermore,

we can also rule out the alternative hypothesis that older participants� poorer mem-

ory performance in the condition with 40 s could be due to a greater delay betweenitem presentation and recall. Results show that old–old adults� different recall perfor-mance in the two conditions, with 20 and 40 s per word, are not due to a difference in

delay between item presentation and recall.

However, it must be noted that also in the 20 s condition, in which generation of

irrelevant detail was reduced significantly, as well as the quality and specification of

images, old participants performed worse than young participants. Therefore, while

there is evidence that irrelevant thoughts, produced rather frequently by old partic-

ipants, influence their memory performance negatively, other variables, such as typeand specification of images are not clearly related to memory performance. In the

present study it was not possible to investigate directly the relationship between type

of image and memory, as spontaneously generated images are examined rather than

a predetermined type of image.

4. General discussion

The aims of the present study were to investigate age differences in image genera-

tion from concrete words and the relationship between type and specification of im-

ages and memory recall. Hence, in Experiments 1 and 2 the types of image generated

were classified and their frequency was compared between age groups. Both experi-

ments found that older participants generated general and self-referred images more

frequently, whilst young participants preferred specific images. However, older adults

did not appear to generate poorer quality images only, although they produced more

general images that can be considered skeleton images from which more complex im-ages may be developed. Older adults also generated more self-referred images. In

many cases, the latter images appear to require generation processes which are par-

tially different from those used in other images. Of particular interest to our study,

they are also reported to produce better recall than other images (Cornoldi et al.,

1989; De Beni & Pazzaglia, 1995; Helstrup, Cornoldi, & De Beni, 1997). It is possible

that in the present research self-referred images contribute significantly to older

adults� memory recall. However a direct control of image generation and memory

it is necessary to confirm this hypothesis. Furthermore, examination of the number


of relevant details associated with each image type did not show marked age-related

differences when no strict time constraints were introduced. Therefore, older adults

appear to spontaneously generate good images, of a quality and specification compa-

rable to those of younger participants, although preferring different image types.

However, in line with Treat and Reese (1976), older adults� image generation per-formance was sensitive to time constraints. Older adults� images were reduced in

quality and specification when less time was available. This result could be explained

either according to the hypothesis of a cognitive slowing with age (see for example,

Salthouse, 1992) or to the hypothesis of a reduction in mnemonic and attentional re-

sources (Craik & Byrd, 1982; Light, 1991). It also fits with Dror and Kosslyn�s (1994)findings that older adults are slower than younger, specifically with imagery pro-

cesses such as image activation and, to some extent, image maintenance, both re-

quired in the task of generating and describing mental images as proposed in thepresent study. Furthermore, according to Hasher and Zacks� (1988) hypothesis thatinhibitory control efficiency decreases with age, older participants introduced a

greater amount of irrelevant details (thoughts) in image description. However, inhib-

itory control does not appear to be related to time constraints as image generation

processes are. In fact, in this case, time works as an external constraint reducing

the opportunity to overload memory and create interference.

Experiments 1 and 2 were also aimed at examining age-related differences in the

memory of words presented, and in the relationship between type and specificationof images generated and memory performance. According to the results of previous

research (see for example, Dirkx & Craik, 1992; Isingrini et al., 1994; Richardson &

Rossan, 1994; and also Mason & Smith, 1977; Witte & Freund, 1976), older adults

are not as good as younger participants in recalling concrete words following imag-

ery coding. In Experiment 1 we found that older participants recalled fewer words

than younger ones. Poorer memory performance did not seem to be related to poorer

encoding as older participants generated good quality images comparable in number

of relevant detail with those generated by younger participants. However, the anal-ysis of irrelevant detail reported in image description showed that older adults had

problems controlling irrelevant information, excluding it from memory. Experiment

2 replicated these results and, in particular, demonstrated that a condition in which

time constraints reduce irrelevant detail, although damaging the quality and specifi-

cation of images generated, increases the memory performance of older adults. The

control of irrelevant thoughts during encoding and maintenance appears to be a fac-

tor significantly related to older adults� memory of concrete words and the sponta-

neously generated corresponding images.Although we agree that the worst cognitive performance of older adults is not

based on a single factor, as argued by Richardson and Rossan (1994), we believe that

the evidence collected in the present study demonstrates that one of the factors affect-

ing older adults� mental functioning is inhibitory control. Our results extend the in-

hibitory control hypothesis to age-related differences in memory performance

following an encoding phase requiring the construction of mental images. However,

the suspected lack of inhibition does not seem to be exclusively related to imagery

processes but, as the irrelevant thoughts recorded appeared quite heterogeneous


(not mainly visual) in nature, it seems to be more general, causing interference in var-

ious memory tasks.

Inhibitory control also may not be the only factor responsible for age-related de-

clines in memory performance. The types of images generated and their specification

seem to be independent of irrelevant detail, although related to memory performance(Cornoldi et al., 1989; De Beni & Pazzaglia, 1995), and differ between age groups.

Experiment 2 demonstrated that a better memory performance by old–old adults

was found in a condition in which time constraints reduced quality and specification

of mental images but also irrelevant thoughts. However, fewer irrelevant thoughts,

although improving older participants� memory performance, did not eliminate

age-related memory differences completely. Therefore, while inhibitory control plays

a critical role, we cannot exclude the influence of other factors such as type of image

or type and efficiency of imagery processes as well. Specific and self-referred imageshave more distinctive and highly associated elements than general images, hence they

should create more efficient cues to improve recall. In support of these predictions,

experimental evidence demonstrates that contextualised images are more memorable

than non-contextualised images (De Beni & Pazzaglia, 1995).

The type of image and type or efficiency of imagery processes seem to be signifi-

cantly related to memory performance, although it cannot be excluded that both

may be influenced by a reduction in cognitive resources or an impairment in inhib-

itory control, or another general factor (Craik, 1994; Hasher & Zacks, 1988; Light,1991). For example, general differences in semantic processing between old and

young people could determine preferences for a particular type of image or could

stimulate the production of details interacting with inhibitory control. Older adults

have been shown to be less likely to report the use of imaginal mediators, preferring a

more verbal coding and processing (Richardson & Rossan, 1994). Future research

should more specifically and directly investigate the relationship between type of

image and memory performance in order to better distinguish the influence of the

former from inhibitory control limitations in age-related memory differences for con-crete words coded under mental imagery instructions.

Acknowledgements

The authors wish to thank Cristina Ceriani and Elena Manzini for their help col-

lecting data. They would also like to thank Francesca Pazzaglia for her precious

comments throughout the research. The authors specifically thank Albert Postma

and the anonymous reviewers for their critical and helpful observations on earlier

drafts of this manuscript.

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When mental images are very detailed: image generation and memory performance as a function of age

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