Visual memory for colour

Acta Psychologica 46 (1980) 103-114

0 North-Holland Publishing Company

VISUAL MEMORY FOR COLOUR

Portia E. FILE University of Dundee, Dundee, Scotland

Accepted October 1979

Two colours were either simultaneously or successively presented. In both cases the time taken to determine whether the colours differed increased as the visual similarity of the colours

increased. In another experiment, colours or names of colours were presented successively in different blocks of trials. Here colour similarity affected the discrimination reaction times

whenever the second stimulus was a colour. This was taken to suggest that visual mnemonic representations can be generated from the first stimulus.

Introduction

Demonstrations of visual memory have frequently been reported in the literature. However, in most studies there has been no attempt to determine whether the relevant mnemonic representations resemble their visually perceived referents to the extent that’they and their perceived referents have the same ordering of values along dimensions.

Some investigations have merely shown that visual stimuli are remembered differently from their verbal labels. Other studies have shown that physically different stimuli are remembered differently even though they have the same label. These studies (e.g. Posner and Mitchell 1967; Bahrick and Bahrick 197 1; Hopkins et al. 1973; Madigan et al.

1972; Swanson et al. 1972), do not provide much information about the extent to which the mnemonic representations resemble the perceived stimuli. For example, Posner and Mitchell showed that when ‘A’ is remembered, the time taken to decide that a newly presented stimulus has the same name is shorter if it is ‘A’ than if it is ‘a’. This study

* Requests for reprints may be sent to: Portia E. File, Dept. of Psychology, University of Dundee, 164 Nethergate, Dundee, Scotland.

103

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shows that, in this task, the mnemonic representations of ‘A’ and ‘a’ differ, but not whether they differ in the same way as the visual perception of ‘A’ and ‘a’. If, for instance, the representation of a letter in perception consists of a set of values on a number of dimensions or features, the study does not show that the set of features used to distinguish perceptual representations is matched by a corresponding set of features used to distinguish mnemonic representations.

Other studies (e.g. Posner et al. 1969; Tversky 1969; Wood 1974) show that the sets of features used to represent stimuli in memory correspond to the sets of features used to perceptually distinguish the stimuli themselves. For example Tversky (1969) found that when subjects determine that a face differs from a face previously memorized (both pictured in an identikit-like format) their reaction times decrease as the number of features which differentiate the faces increases. In this study a feature was, for example, the condition of the eyes of the face, these being open or closed. Such studies of multidimensional stimuli suggest a correspondence of feature differentiation in memory and perception. However, since stimuli in these studies vary in the number of features which differ rather than in the difference between values on a single feature, these studies do not indicate the extent to which the values along individual features or dimensions are commonly represented. Thus in Tversky’s experiment the features of the stored face could be remembered as the verbal descriptions open or closed eyes, and smiling or straight mouth, yet the observed relationship between visual difference and discrimination reaction time could still be obtained.

A resemblance between representations for different values along a single dimension and their perceived referents has been demonstrated by Moyer and Bayer (1976). When subjects are given the names of two circles the time taken to determine which circle is the larger decreases as the difference in size of the circles increases. This relationship also obtains when the circles themselves are shown to the subjects, instead of the names.

The present study was designed to confirm the equivalence of mnemonic and perceptual dimensions. Such equivalence defines visual memory in a strong sense. For both memorized and perceived colours the time taken to determine that two colours differ was compared when the colours were similar and when they were dissimilar. If colours are mnemonically represented as in perception, discrimination RTs based on memory should be like those based on perception. Welford (1960) has

P.E. File / Visual memory for colour 105

summarised studies showing that perceptual discriminations between similar items take longer than perceptual discriminations between dissimilar items. RTs based on both the perception and memory of colours might therefore be expected to show this characteristic.

Experiment 1

The first experiment had two aims: first, to confirm the finding that discrimination

reaction time in perception (i.e. when the colours are presented simultaneously) increases with increases in the similarity of the colours (Welford 1960); second, to determine whether this same relationship is obtained when one of the colours is presented after the presentation and removal of the other (successive presentation): if the first colour is remembered visually the same relationship should be obtained; if the colour is not remembered visually, there should be no effect of colour similarity on reaction time; if the visual representation is of short duration as suggested by Posner et al. (1969) the effect of colour similarity on reaction time should decline

as the interval between presentation of the two colours increases.

Method

Subjects

Twelve volunteers from the students and staff of the University of Dundee were paid 75p for participating in the experiment. They were tested individually in 75 mm sessions. The Ss were screened for colour blindness with the Ishihara Test for Colour Blindness (Ishihara 1969).

Stimuli

Six colours: red, orange, yellow, green, blue and purple were chosen to represent the six common single word colour word labels. Colours with distinctive word labels were chosen so that colour similarity would not correspond to label similarity as it might with some colour sets (e.g. red, red-orange, orange, yellow-orange). An example for each label was made, using coloured slides. As far as possible, these examples were chosen to minimize brightness and saturation differences between them. Using visual interpolation from the Munsell Book of Color (Kelly 1955), three judges, the experimenter and two members of the Psychology Department, agreed on the Munsell notation of the six colours. These notations are listed in table 1. For each colour pair, colour differences in three dimensional colour space, were calculated using Godlove’s (195 1) equation.

Procedure

Each S was required to determine whether two colours were the same or different. If the colours were the same, S pressed the right-hand ‘same’ button; if the colours were different, S pressed the left-hand ‘different’ button. The two colours were presented on two IEE One Plane Readouts. These present any of twelve stimuli on a

106, P.E. File / Visual memory for colour

Table 1

The Munsell notations of the colours used in the experiments.

Colour II ue Brightness (value) Saturation (chroma)

Red 5.OR 5 11

Oranpc 5.OYR 7 10

Yellow 5.OY 8 10

Green 3.5G 6 10

I~lue 2.5PB 4 8

Purple 6.5P 5 10

small screen by means of a set of lenses. The Readouts were placed one on top of

the other at a visual angle of two degrees by two degrees for each colour and with

a visual angle of four degrees between their adjacent edges. In the successive conditions, the first colour was presented on the upper display and the second colour was presented on the lower display.

In the successive conditions a trial consisted of a 0.5 set presentation of the first (memory) colour, the inter-stimulus interval (ISI), a 0.5 set presentation of the

Table 2 The differences between the colours in three-dimensional colour space and the level of the rank

order of the colour similarity variable (CS) for each colour pair.

Colour one Colour two Colour similarity

level (CS)

A colour

Blue

Purple Red

Orange Yellow

Green

Mean

Blue

Purple Red

Orange

Yellow Green

Mean

Blue Purple Red Mean

Purple Red

Orange

Yellow Green

Blue

Red

Orange

Yellow

Green Blue

Purple

Orange

Yellow Green

1

2 2 2 2 2

2 2

3 3 3 3

9.3 11.0 10.3

7.4 13.6 16.4 11.3

16.8 17.2 17.2 16.1 24.0 20.0 18.6

21.2 22.0 20.1 21.1


second (test) colour and a 2.5 set interval before the next trial. The five ISIS in the successive conditions were: 0.0 set, 0.5 set, 1.0 set, 2.5 set and 4.5 sec. In the simultaneous condition, a trial consisted of a 0.5 set presentation of the two col-

ours followed by a 2.5 set interval before the next trial. (The simultaneous condition therefore differed from the 0.0 set successive condition in that the colours were presented concurrently rather than one following the offset Gf the other). Each of the six levels of IS1 (five successive and one simultaneous) were blocked. Ss were told the interval between presentations before the start of each block. The S’s reaction time (RT) was measured from the onset of the test colour, or in the simultaneous condition, from the onset of both colours.

All 36 possible colour pairs were used at each level of ISI. Six sequences of the pairs were constructed by random selection with the constraint that each pair appear three times. One-sixth of the trials required ‘same’ responses and five-sixths required ‘different’ responses. For each S a different colour sequence was used for

each of the six levels of ISI. Two unsystematic digram balanced latin squares were chosen to determine the

order of presentation of the IS1 blocks. All six Ss in each latin square received the same order of presentation of the colour sequences, but the order was different between the two latin squares.

Twelve practice trials were presented at the beginning of the experiment and these practice trials were also given at the beginning of each IS1 block. The colour pairs used in the practice trials were chosen randomly with the constraint that each colour be used at least once.

Stimulus sequencing was controlled by a tape reader and intervals were controlled by relays and timers. Reaction times were measured by a Solarotron Fre- quency Counter EM1 616 and were recorded by an ADD0 Punch. Responses were recorded by the experimenter.

Results and discussion

A mean of the three RTs to each colour pair excluding erroneous responses was determined for each S. Data analyses were performed on these means.

To determine the relationship between colour similarity and RT the variable of colour similarity (CS) was used rather than colour space differences. The colour similarity value of each pair given in table 2 is found by adding one to the number of experimental colours with hue values between those of the members of the pair. For example, red-orange and blue-green are CSl and red-green and purple-yellow are CS3. This colour similarity variable has the desirable characteristic that every colour is included equally often at each level of colour similarity so differences in the perception or memory of individual colours should not influence the effect of similarity measured by CS. An analysis of variance of mean RTs for the same responses of each subject to each colour at each IS1 confirmed that there were differences in RTs to different colours, F(5, 55) = 2.972, p < 0.05, though these differences did not interact with ISI, P’(25, 275) = 1.276.

For each S, a mean of the mean RTs for different colour pairs was calculated for each level of colour similarity for each ISI. (See fig. 1 and table 3 for overall means

108 P.E. File / Visual memory for colour

‘\_. 2.5SEC ISI

:-----v.__ 0.5SEC ISI

\

I\:; “s:&itEO”S

I I I , I

0 10’ 1 I

CSl C&S3

COLOUR -SIMILARITY (CS)

Fig. 1. RT colour similarity functions for each level of ISI in experiment 1.

and error rates.) Using these means, a two-way within-subject analysis of variance with colour similarity and ISI (3 X 6) was performed. Only the main effect of colour similarity was significant, F(2, 22) = 10.1, p < 0.001. These results show that discrimination RT is sensitive to the magnitude of colour differences even when the colours are as dissimilar as those used in the present experiment. The significant main effect of colour similarity is primarily due to the increase in discrimination RT as the similarity of the colours increases. (If mean colour space distances are used, the trend appears to be linear and to account for 99% of the variance of this effect which is significant; F( 1, 1 1) = 1 1.7 1, p < 0.0 1.)

This effect of colour similarity does not appear to interact with the length of the

Table 3 Percentage errors for experiment 1.

ISI Colour similarity level

1 2 3

Simultaneous 0.23 0.00 0.00 0.0 set 0.00 0.46 0.93 0.5 set 0.00 0.00 0.00 1.0 set 0.46 0.00 1.39 2.5 set 0.00 0.93 0.46 4.5 set 0.69 0.69 0.46


interstimulus interval, F( 10, 1 10) = 0.503. As can be seen from the linear regression equations for RT as a function of colour similarity plotted in fig. 1, for each memory interval the greater the colour similarity of the items to be discriminated, the longer the discrimination RT. This provides evidence for visual memory. In their effect, the similarity between a memorized colour and a perceived test colour resembled the similarity between the two simultaneously perceived colours. For each retention interval, the successive discrimination was apparently performed using mnemonic representations of colour that resembled the perceptual representations of colour.

For different responses the main effect of ISI was not significant F(5, 55) = 1.30. However, the effect was significant for same responsesF(5, 55) = 5.765, p < 0.001. As IS1 increases, there is a monotonic increase in RT (from 477.6 msec to 586.5 msec) apart from the simultaneous condition (548.5 msec).

Experiment 2

Several investigations have shown that Ss can generate internal representations of stimuli which in some sense resemble the visually perceived stimuli themselves. However, demonstrations of the generation of visual representations are often subject to the same qualifications as demonstrations of memory for visual representations: they show only that internal representations of stimuli can be generated which are distinguished by the same number of features or dimensions which distinguish the visually perceived stimuli themselves. For example, Tversky (1969) showed that the greater the number of different features in the stimuli the greater the difference in their generated representations. The present experiment was designed to show that mnemonic representations can be generated which have the same ordering of values within dimensions as their perceived referents; the greater the distance between values in the referent, the greater the difference in the mnemonic representation. Both colours and colour words were used as memory and as test stimuli. If visual mnemonic representations are generated in the form of the test item, discrimination RT should increase as colour similarity increases when the test item is a colour even when the memory item is a colour word. If, on the other hand, visual mnemonic representations are only possible when the visual information is actually presented, the correlation between colour similarity and discrimination RT should only be obtained when the memory item is a colour.

Method

Subjects

Twelve volunteers from the staff and students of the University of Dundee were paid 75p for participating in the experiment. The Ss were tested individually in 75 min sessions. They were screened for colour blindness with the Ishihara Test for Colour Blindness (Ishihara 1969).

110 I?I:‘. File / Visual memory for colour

Stitn uli The six colours used in experiment 1 were presented on the upper One-Plane Read- out and the names of these colours, printed in black on a transparent background, were presented on the lower One-Plane Readout at a visual angle of 0.4 degrees per letter.

Procedure The procedure used in the sequential conditions of experiment 1 was used in the present experiment except that the ISI was always 4.5 set and’the memory and test stimuli could be either colours or colour words. The four combinations of memory format (colour or word) and test format (colour or word) were presented in blocks of 120 trials. Ss were informed of the format of stimuli at the beginning of each block. Three digram balanced latin squares were chosen randomly to determine the presentation order of these blocks for each S. Four of the six colour sequences constructed for experiment 1 were randomly selected for use in the present experiment. For each latin square determining the block presentation sequences, one order of presentation for the colour sequences was randomly chosen and was used for all four Ss in the latin square. The apparatus was the same as the apparatus in experiment 1.

Results and discussiotz

For each S, a mean was calculated for each different colour pair in each memory format by test format block, excluding erroneous responses. A mean of these means was calculated for each level of colour similarity for each block. (See fig. 3 and table 4 for overall means and error rates.) A within-subjects analysis of variance with three factors: memory format, test format and colour similarity (2 X 2 X 3), was performed on these means. The main effects for test format and colour similarity were significant; I;yl, ll)= 15.3, p<O.Ol for test format; F(2, 22)=6.91, p < 0.01 for colour similarity. Two interactions were significant: test format X colour similarity f7(2, 22) = 22.1, p < 0.001, and memory format X test format,

f;‘( 1, 11) = 5.02, p < 0.05. The condition in which both memory and test formats were colours is similar to

the 4.5 IS1 condition of experiment 1. The relationship between RT as a function of colour space distance in this condition resembles the relationship obtained for the simultaneous, perceptual discrimination condition in experiment 1. (See figs. 1 and 2.) This finding that the similarity of mnemonic representations, as indicated by variations in discrimination RT, resembles the similarity of visually perceived colours supports the conclusion that visual mnemonic representations are available for at least 4.5 sec.

The data from the present experiment also suggest that visual colour representations can be generated. The effect of colour similarity depends upon the test format. If the test items were colours then, regardless of the format of the memory items, an effect of similarity was obtained. If the test items were words, there was no effect of similarity. These findings are indicated by the significant interaction of colour similarity with test format. They can also be seen in fig. 7 in which KT for

P.E. File / Visual memory for cdour 111

WORD-WORD

COLOUR -COLOuR

““o.,.. CSl cs2 %3

CoLouR-S~IILARITY (CSI

Fig. 2. RT colour similarity functions for each memory format by test format condition in experiment 2.

each condition is plotted as a function of colour space distance. RT decreased monotonically as the colour similarity decreased when the test stimuli were colours but not when they were words.

The significant interaction of memory format by test format is of some interest. Even though Ss always knew what test format to expect, they took longer when the memory format was different from the test format.

An analysis of variance was also performed on the mean RTs for same responses of each subject in each condition. The only significant effect was the interaction of memory format X test format, F( 1, 11) = 5.988, p < 0.05. The overall means were 534 msec for Colour-Colour, 560 msec for Word-Colour, 581 msec for Colour-Word and 564 msec for Word-Word conditions. As with the different responses, longer RTs were obtained when the memory format was different from the test format.

Table 4 Percentage errors for experiment 2.

Memory format Test format Colour similarity level

1 2 3

Colour Colour 0.93 0.93 0.46 Word Colour 2.08 0.23 0.00 Colour Word 0.93 1.39 0.46 Word Word 0.93 0.46 0.93

112 P.E. File / Visual memory for colour

General discussion

The present experiments investigated the mnemonic representations of colours after relatively short retention intervals by examining the effects of colour similarity on discrimination RT. Unlike Tversky’s ( 1969) stimuli, the colours used in this experiment do not vary in the number of dimensions which differ but in the distance between them on the colour dimension [ I]. The results suggest that mnemonic representations that preserve the similarity relationships among visually perceived colours are available for at least 4.5 set and that such representations can be generated.

The results support Heider and Olivier’s ( 1972) conclusion that colours can be represented visually in memory. They appear to be inconsistent with Lantz and Stefflre’s (1964) and Brown and Lenne- berg’s (1954) conclusion that colours are remembered verbally; however, colours may have multiple representations. Number of colours to be remembered may be one determinant of the type of representation used in a particular instance. The memory for only one colour was tested in each trial of both Heider and Olivier’s experiment and the present experiment. Lantz and Stefflre found less evidence for verbal mnemonic representations when one rather than four colours were tested.

The mnemonic representations indicated by the present experiments are visual in the sense that they have the similarity relationships of their visually perceived referents. This does not, it should be noted, mean that the representations are analogue rather than symbolic in format. Since it has not been demonstrated that perceptual representations are analogue, a deinonstration that mnemonic representations are the same as perceptual representations does not show that mnemonic representations are analogue (see Wilton 1978).

The dependence df the colour similarity effect on the format of the

[l] The colours in this experiment do differ on four dimensions: colour, hue, saturation and

brightness (see table 1). Hue differences between colours are so great that they virtually determine colour difference (rs = +0.90). Correlations of reaction times for different colour pairs in Experiment 1 with each dimension were calculated for each subject. A one-way analysis of variance performed on these correlations showed a significant difference in dimensions, F(3, 33) = 9.4, p < 0.001. The means of the correlations for each dimension averaged across Ss (-0.51, -0.52, -0.17, -0.12 for colour, hue, saturation and brightness, respectively) were compared

using a Newman-Keuls test. The correlations between hue and colour were not significantly different but all other differences were significant. This suggests that subjects primarily use colour

(or hue) to make their decision. See Linde and Paivio (1979) for a similar conclusion.


test stimulus is evidence that visual mnemonic representations can be generated. When a memory word is tested by a colour, then a mnemonic representation which produces similarity relationships of colours is generated. When a memory colour is tested by a word, then a mnemonic representation which does not produce the similarity relationships of colours is used. Tversky (1969) and Wood (1974) have also shown that similarity effects depend on the format of the test stimulus.

The slower RTs when the format of memory and test format differ have also been found by other experimenters (e.g. Swanson et al. 1972; Burrows 1972). Wood (1974) found the reverse effect which he suggests may be due to his shorter ISI. In the present experiment, since subjects knew the format of the test item in advance they could have generated in advance a mnemonic representation appropriate for matching it. The longer RTs for conditions in which memory and test formats differ suggest that the generation may have been delayed until the test stimulus was presented. Alternatively, the generated representations may not have been as good as representations derived from the stimuli and the comparisons using these poorer quality representations may therefore have been slower. The degraded representation used in these conditions might be expected to affect more difficult comparisons most, increasing the slope of the relationship between colour similarity and RT. A comparison of the trends between RT and colour similarity for Colour-Colour and Colour-Word conditions indicated that the Colour-Word slope is significantly steeper than that of the Colour- Colour condition, E’( 1, 22) = 7.94, p < 0.05 as would be expected if this latter interpretation is correct.

The representations of different dimensions in memory seem to be similar in that the ordering of values along any dimension affects reaction times in similar ways. For example, Moyer’s ( 1973) and Moyer and Bayer’s (1976) observations that reaction times decrease with increasing differences in size between two objects has also been shown for a variety of other dimensions (e.g. Moyer and Landauer 1973; Restle 1970; Kerst and Howard 1977). A distinction of type between visual and non-visual representations is therefore probably not warranted in memory research; abstract dimensions and the source of a representation, whether sensation or abstraction, seems unimportant for the way it functions in memory.

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Documents

Visual memory for colour