Neuropsychologia, 1977, Vol. 15, pp. 61 to 67. Pergamon Press, Printed in England.

ATTENTION, AWARENESS, A N D HEMISPHERIC DIFFERENCES IN WORD RECOGNITION

GEOFFREY UNDERWOOD

Department of Psychology, University of Nottingham, Nottingham NG7 2RD, England

(Received 17 November 1975)

Abstract--When subjects attend to the task of naming a briefly presented picture, their naming latencies are affected by a word presented by the side of the picture whether they are able to recognise the word or not. For unreported words the effect is stronger with related than with unrelated words, but this is reversed for words which enter awareness. Moreover, this relationship is largely a left hemisphere function. Two levels of interference are apparent in this experiment: an effect of related words which retard the picture naming latency, which operates at a pre-attentive stage of processing, and a further effect of phonemic or articulatory competi- tion which operates as the identity of the printed word is available to awareness.

INTRODUCTION

IT APPEARS that attention is not necessary for printed or spoken words to be recognised. Dichotic listening studies have provided evidence of the effects of words in the secondary message when attention was directed to the primary message, and when the listener claimed not to be aware of the effective words [1-5]. Similar results have been demonstrated for the case of visually presented words and sentences. WILLOWS and MACKINNON [6] reported that the comprehension of lines of text which were read aloud by their subjects was affected by words printed between these lines and which were described as "irrelevant". Although subjects could not recall these irrelevant words, they did affect the outcomes of multi- choice questions concerning the meaning of the attended prose. The unattended words which influenced the interpretation of the passage were related to the prose, and similar results have been reported using tachistoscopic presentation. BRADSHAW [7] briefly pre- sented two words at the same instant as a fixated ambiguous word, one word on either side, and asked his subjects to interpret the fixated word. When a word related to the ambiguous word was presented, the interpretation was accordingly affected, even when the disambiguating word could not be recalled after exposure. An unattended word related to the ongoing activity appears to be effective upon that activity, but there exists a complex relationship between the effect and the affected. UNDERWOOD [8] investigated this relation- ship using a tachistoscopic picture-naming task. Subjects attended to the task of naming vocally a simple line-drawing from a previously learnt set. During the same exposure a single word was presented. The word was related either to the picture being shown, or was semantically unrelated. Related words consistently slowed down the naming response to the picture (in comparison with those trials in which no word was presented), but the effect of unrelated words depended upon the attentional strategy demanded by the task. With no spatial uncertainty about the picture, thereby allowing a strategy of focused attention to its impending location, an unrelated word was ineffective. When the picture might appear to the left or to the right of fixation, an unrelated word was more effective than a

61

62 GEOFFREY UNDERWOOD

related word. In the la t ter case, subjects were not able to focus their a t tent ion and had to accept more in format ion f rom the irrelevant word. When at tent ion was focused, the related words may have been processed as a consequence o f the recogni t ion of the picture. The generat ion o f the picture name would act to lower the recognit ion threshold of all re la ted words, and act ivat ion of the lexical representa t ion of the word may in turn have interfered with fur ther processing of the picture name. A n al ternat ive hypothesis is that the focusing of a t tent ion inhibits or a t tenuates [9] the processing of all per iphera l stimuli but tha t recogni t ion pr io r to awareness proceeds regardless. The a t tenua ted recogni t ion o f a word would be sufficient to interfere with the processing of a related name, bu t not with the processing o f an unre la ted name. The division of a t tent ion between two locat ions may serve to increase the amoun t of st imulus in format ion avai lable abou t the irrelevant word by either of our hypotheses. To provide more evidence abou t these two hypotheses of the route o f semant ic interference, the exper iment to be described here demanded a focused a t tent ion strategy f rom the observers, and tested for awareness of the i r re levant word immedia te ly after comple t ion of the picture naming task on each trial. More related than unre la ted words should be avai lable for repor t by the first hypothesis , by which contextual in format ion lowers the recogni t ion threshold of the irrelevant word, but no difference is predic ted by the second hypothesis , by which lexical exci ta t ion of all i rrelevant words is postulated. These models will be described as the contextual faci l i tat ion hypothesis and the a t tenua ted recogni t ion hypothesis respectively, but it should be noted that they are no t mutua l ly exclusive.

UNDERWOOD [8] also repor ted a visual field effect in the divided a t tent ion exper iment ment ioned above, and this effect was investigated further by the present experiment . Whereas an unre la ted word causes more interference than a related word when the words were projec ted to the subject 's left cerebral hemisphere, this difference was unrel iable when words were presented to the r ight hemisphere. This interact ion was possibly a result o f super ior percept ion of verbal mater ia l presented to the left hemisphere, as certain evidence would suggest [10-12], but we cannot exclude the possibi l i ty of lexical processing in both hemispheres [13] and the interact ion result ing f rom phonemic or a r t icu la tory interference only when words are presented to the left hemisphere. Fur the r evidence on the awareness which the observers repor ted for the i r relevant words was sought as being per t inent to these hypotheses, for phonemic or a r t icu la tory encoding would be expected to be associated with entry to awareness more than would lexical contac t pr ior to encoding.

M E T H O D Apparatus and materials

Ten line drawings taken from a children's reading book were copied and used throughout the experiment. The drawings represented a bird, a boat, a car, a cat, a chair, a fish, a house, a lemon, a pan, and a train, and each subtended approximately 2 ° of horizontal visual angle when viewed through the tachistoscope used (Scientific Prototype model GB). The vertical boundaries subtended between 1 ° and 2 °. Eight copies of each picture were taken and pasted on to white tachistoscope cards. Four copies of each picture were pasted to the left of the cards, and 4 to the right. A word was printed to one side of the picture on each card. Half of the words were semantically related to the pictures, and half were unrelated. These stimuli were collated for a 2 × 2 factorial design, where the factors were field of visual projection (left or right) and semantic relatedness of the word and picture (related or unrelated), and so only four presentations might appear to be the minimum required. An effect in one visual field but not the other could not then be ascribed to differential hemispheric processing, for the effect could be a function of the particular set of words selected [14]. To alleviate this problem the same set of words was presented to both hemispheres overall, using two groups of subjects. A word was never used twice with the same subject because the continued processing required by asking the subject to report any words seen might lead to a sensitisation effect apparent on retesting.

ATTENTION, AWARENESS, AND HEMISPHERIC DIFFERENCES IN WORD RECOGNITION 63

It was not considered necessary to control here for the possibility of any interference effect being a result of visual distraction, as this was found not to be the case in the previous experiment [8]. In the focused attention experiment, the increase in picture naming latency resulting from adding an unrelated word to an otherwise blank card was negligible.

The words were printed using 18 pt Letraset (sheet 287) in lower case. Words were located alongside the midpoint of the picture, and with eye fixation in the centre of the picture the outside letter of the longest word subtended 3{ -o from the centre of fixation, and the inner letter of each word subtended 1½ ° from the centre of fixation. Words varied in length between 4 and 7 letters, each related word associated with any picture being matched with an unrelated word of similar length and frequency.

The onset of exposure of the card in the tachistoscope started a msec timer which was in turn stopped by the subject vocalising a response into a microphone which triggered a voice switch.

Subjects Twelve students (7 females and 5 males) from the University of Waterloo participated in the experiment

on a volunteer basis. All had normal or corrected-to-normal vision and none had difficulty in recognising or naming any of the pictures at the experimental exposure used, when tested in a practice period. All subjects claimed to be right-handed, but they were not given any objective tests of laterality.

Procedure Subjects were tested individually with a repeated measures design, each subject providing a response to

each of the 10 pictures in 4 conditions: related and unrelated words presented to left and right hemispheres. Six subjects were allocated to each stimulus control group: one group received one set of words to the right hemisphere and the other group received that set of words to the left hemisphere. The hemisphere of pro- jection was determined by an ABBA-BAAB counterbalancing procedure. Half of the subjects in each stimulus control group received 20 trials in which the word was printed to the right of the picture, followed by 40 trials of words in the left visual field, followed by a further 20 trials of words in the right visual field. The other half of the subjects received the corresponding blocked presentations. Within each block of trials the order of trials was randomised for each subject.

A trial consisted of the experimenter uttering a warning of the imminence of a picture, followed by a 60 msec exposure of picture and word. The response required of the subjects was the name of the picture as quickly as possible. They were then required to offer the name of the word which accompanied the picture as "often as possible during the experiment, but without allowing this to impede the picture-naming task". Prior to the experiment the subjects were familiarised with the pictures and the names required. Fifteen practice trials were given prior to the first block of trials, and a further 5 practice trials prior to the visual tield changes during the course of the experiment.

The pre-test and post-test fields of the tachistoscope were illuminated and blank, and two horizontal lines in these fields indicated to the subjects the upper and lower boundaries of the set of drawings, together with their horizontal extents. Subjects were instructed to fixate between these lines on hearing the warning between each trial, and to attend "first and foremost to the picture-naming task".

The latency of the naming of the picture on each trial was recorded, together with the word recognition response whenever offered. Accuracy of picture naming was emphasised to the subjects, and trials on which erroneous responses were offered were not repeated so as to control the total exposure period of each word.

R E S U L T S

N a m i n g response e r ro rs were r e c o r d e d on less t h a n 4 ~o o f the trials, were d i s t r ibu ted

even ly o v e r all cond i t ions , and cons i s ted la rge ly o f the subjec t u t t e r ing the w o r d in pre-

fe rence to the p ic ture name . T h e re sponse la tencies are p resen ted in Tab l e 1, and the ten

la tencies f r o m each subject wi th in each c o n d i t i o n were ave raged and submi t t ed to an

analysis o f var iance . The occu r r ence o f e r r o n e o u s responses and the d iv is ion o f la tency

responses in to those a c c o m p a n i e d by w o r d recogn i t ion , a n d those n o t so a c c o m p a n i e d ,

resu l ted in ceils wi th u n e v e n entries. S o m e subjects neve r r e p o r t e d the words in ce r ta in condi t ions . T h e r e were th i r t een ins tances o f e m p t y cells f r o m the to t a l o f n inety-s ix cells

r equ i r ed by the analysis , as a resul t o f this t r ea tment . T h e e x t r a p o l a t i o n p r o c e d u r e de-

scr ibed by WINER [15] fo r r ep lac ing miss ing d a t a was used to c o m p l e t e the cells in this instance.

T h e n a m i n g la tency w h e n w o r d s were p re sen ted to the lef t h e m i s p h e r e was f o u n d to be

g rea te r t h a n w h e n they were p re sen ted to the r igh t h e m i s p h e r e ( F = 9-3; d f = 1, P < 0.025)

64 GEOFFREY UNDERWOOD

Table 1. Mean response latencies (msec) and standard deviations from the picture naming task

Related word Unrelated word Unattended stimulus Reported Not reported Reported Not reported Printed word in right visual field

Mean = 711 700 860 665 S.D. = 96 81 117 92

Printed word in left visual field

Mean = 745 654 775 661 S.D. = 108 94 105 101

Pictures were named faster when they were accompanied by related words than by un- related words (F = 5.5; df = I, 11 ; P < 0.05), and when the word was reported the picture naming latency was greater than when the subject claimed to be unable to respond (F = 115.4; df = 1, 11; P <: 0.001). However, each of these main effects are involved in inter- actions and so these generalisations are not particularly useful. For related words, those reported cause increased latencies over those unreported, but for unrelated words this effect is magnified (F = 17.1; df = 1, 11; P < 0.005). The faster naming responses for pictures with reported related words over those responses associated with reported un- related words, holds mainly for words projected to the left hemisphere. Awareness of a related word results in only a slightly slower response than absence of awareness here whereas unrelated words projected to either hemisphere, and related words to the right hemisphere all result in considerably slower naming responses as a consequence of their entry to awareness (three-way interaction of visual field x semantic association of picture and word x reporting o f word: F = 10.4; df= 1, 11; P < 0.01), as indicated by the latency data in Table 1. Indications of the consistency of these effects are given by looking at the number of subjects showing trends in the directions found to be statistically reliable. For words which were reported, 11 out o f 12 subjects gave average naming responses with unrelated words slower than those with related words. For unreported words, 8 out of the 12 subjects gave slower responses with related words than with unrelated words.

The incidence o f word recognition responses was also noted, and these data are presented in Table 2. Application of t tart ley's F max test indicated inhomogeneity of variance in these data (F max = 7-44; df =- 4, 11 ; P < 0.05) and so two t-tests were performed, tests

Table 2. Mean percentages and standard deviations of printed words being recognised

Unattended Related Unrelated stimulus word word

Printed word in right visual field

Mean = 31.6 14.2 S.D. = 24.4 19.8

Printed word in left visual field

Mean = 21"6 9.2 S.D. = 11"9 11"7

which are relatively less sensitive to unequal variances. More related than unrelated words were reported during all trials (t ----- 4.31 ; df = 11 ; P < 0.005), but the difference between

ATTENTION, AWARENESS, AND HEMISPHERIC DIFFERENCES IN WORD RECOGNITION 65

presentations of words to left hemispheres and right hemispheres proved unreliable (t = 1.24; af= 11).

DISCUSSION

The naming latency data confirm the effect reported by UNDERWOOD [8] for instances where unattended words affect on-going activities and remain unavailable to awareness. We shall first consider the presentation of words to the subjects' left hemispheres. For unreported words more interference was caused by those which were related to the picture than those which were not. This relationship was reversed however for those cases where the subject was able to correctly identify the word. This suggests an interference effect influenced by several factors, not the least of which is the role played by the articulatory output centres of the left hemisphere. The articulation of the name of the picture was retarded when a phonemic representation of the unrelated word was available, but largely unaffected by the availability of a related word. This might simply be an effect of ease of articulation of semantically related words as a function of their previous association, or it may reflect different routes of interference. Of the two interference hypotheses under discussion here, the contextual facilitation model and the attenuated recognition model, either could provide adequate post hoc explanations of the data, for subjects were quite evidently attempting to recognise the words despite instructions to attend "first and foremost to the picture-naming task". This is indicated by the increased naming latencies in com- parison with the previous focused attention experiment. Most parsimonious with this obser- vation would be the attenuated recognition model, which argues that all words activate their lexical representations, at some level, but that this activation is reduced in comparison with an attended word. Hence the difference between a reported related word and an unreported related word is small, for the effect does not require articulation to manifest itself, but the difference between a reported unrelated word and an unreported unrelated word is large, for the only interference caused by an unrelated word is articulatory. The contextual facilitation model accounts for the interfering effects of related words by the same mechanisms as would its opponent model, but can only account for the effect of a reported unrelated word by arguing that these words were perceived during the direction of attention to them. The consequences of directing attention to the word rather than the picture would be an increase in the naming latency of the picture (as there was), and an increase in the interference effects (as there was) by articulatory response competition. This model cannot explain why the diversion of attention away from the picture should only result in interference when the word is unrelated to the picture.

Support for the attenuated recognition model does not come from the word recognition data of this experiment: more related than unrelated words were reported, as predicted by the contextual facilitation model. Reduced stimulus information may have excited the lexical representations of all unattended words, but the activation of contextually related representations appears to have aided entry of the printed words into awareness. It seems likely that some of the related word 'recognitions' were guesses, for subjects occasionally (less than 3 ~ of all responses) offered words as recognitions which were not presented, but which were semantically related to the picture. As these incorrect responses were offered approximately twice as often when the word was related to the picture than when it was unrelated, it appears that the related word was influencing the guessing behaviour even though the subject was unable to report that word. In accordance with views of the possibilities of classification prior to identification [16, 17] the word may have contacted

66 GEOFFREY UNDERWOOD

its lexical representation in memory with that excitation then spreading to associated items. A set of associations would then be activated prior to the observer being aware o f the identity of the particular stimulus presented.

The naming latency data f rom presentations of words to the right hemisphere are rather more easily interpreted than those f rom left hemisphere presentations. For the cases of both semantically related and unrelated words the entry to awareness and phonemic availability o f a word increased the naming latency of the accompanying picture. It is o f some interest that the interference caused by a related word was restricted to left hemi- sphere presentations for unreported instances, but that for reported instances a presentation to the right hemisphere was more disruptive. F rom the first observation it may be concluded that the lexicon is specific to the left hemisphere (for right handed observers), and f rom the second observation that there are indeed two levels of interference operating in this experi- ment. Related words produce a certain degree o f interference when presented to the left hemisphere, whether reported or not, but when any word is available to awareness as the subject is at tempting to name a picture then even more interference is experienced. These two levels o f interference may then be described as being a function of semantic processing and of articulatory competi t ion respectively.

Semantic processing of picture name and word identity at the same point in time may lead to interference according to MEYER and SCHVANEVELDT'S [18] location search model. I f two lexical representations are activated at the same instant then the task of responding to the pr imary stimulus will be made more difficult if the secondary stimulus activates a representation in a nearby location. If we identify stimuli by directing our attention to activated category locations, then discriminating between two items within a category would lead to a slower response than would discriminating between two semantically unrelated stimuli. This model of the word recognition process (see also [19, 20]) offers a compromise between the response-selection [21] and perceptual-selection [9] theories o f selective attention. Attention has a facilitatory role in the word recognition process, but at tenuation o f a stimulus will not prevent recognition and consequent effects upon on-going behaviour.

Acknowledgements This experiment was performed while the author was on leave of absence at the Univer- sity of Waterloo, and was aided by support from a National Research Council of Canada Grant (No. A-95) to M. P. BRYDEN. Thanks are due to PHIL BRYDEN, NEVILLE MORAY and JOEL SINGER for their comments on various points discussed here.

R E F E R E N C E S

1. CORTEEN, R. S. and WOOD, B. Autonomic responses to shock associated words in an unattended channel. J. exp. Psychol. 94, 308-313, 1972.

2. LEwis, J. L. Semantic processing of unattended messages using dichotic listening. J. exp. Psychol. 85, 225-228, 1970.

3. MACKAY, D. G. Aspects of the theory of comprehension, memory and attention. Q. Jl exp. Psychol. 25, 22-40, 1973.

4. SMITH, M. C. and GROEN, M. Evidence for semantic analysis of unattended verbal items. J. exp. Psychol. 595-603, 1974.

5. TREISMAN, A. M., SQUIRE, R. and GREEN, J. Semantic processing in dichotic listening? A replication. Memory and Cognition 2, 641-646, 1974.

6. WILLOWS, D. M. and MACKINNON, G. E. Selective reading: attention to the "unattended" lines. Can. J. Psychol. 37, 292 304, 1973.

7. BRADSHAW, J. L. Peripherally presented and unreported words may bias the perceived meaning of a centrally fixated homograph. J. exp. Psyckol. 103, 1200-1202, 1974.

8. UNDERWOOD, G. Semantic interference from unattended printed words. Br. J. Psychol., to be published.

ATTENTION, AWARENESS, AND HEMISPHERIC DIFFERENCES IN WORD RECOGNITION 67

9. TREISMAN, A. M. Contextual cues in selective listening. Q. Jl exp. Psychol. 12, 242-248, 1960. 10. BRYDEN, M. P. Tachistoscopic recognition, handedness, and cerebral dominance. Neuropsychologia 3,

1-8, 1965. 11. HERON, W. Perception as a function of retinal locus and attention. Am. J. Psychol. 70, 38~8, 1957. 12. KIMURA, D. Dual functional asymmetry of the brain in visual perception. Neuropsychologia 4, 275-285,

1966. 13. GAZZANIGA, M. S. and SPERRY, R. W. Language after section of the cerebral commissures. Brain 90,

131-148, 1967. 14. CLARK, H. H. The language-as-fixed-effect fallacy: A critique of language statistics in psychological

research. J. verb. Learn. verb. Behav. 12, 335-359, 1973. 15. WINER, B. J. StatisticalPrinciples ht ExperimentalDesign, p. 487. McGraw-Hill, New York, 1971. 16. BRAND, J. Classification without identification in visual search. Q. Jlexp. Psychol. 23, 178-186, 1971. 17. INGLING, N. W. Categorisation: A mechanism for rapid information processing. J. exp. Psychol. 94,

239-243, 1971. 18. MEYER, D. E. and SCHVANEVELDT, R. W. Facilitation in recognising pairs of words: Evidence of a

dependence between retrieval operations. J. exp. Psychol. 90, 227-234, 1971. 19. DIxoN, N. F. Subliminal Perception: The Nature of a Controversy. McGraw-Hill, London, 1971. 20. UNDERWOOD, G. Attention and Memory. Pergamon Press, Oxford, 1976. 21. DELrrscH, J. A. and DEUTSCH, D. Attention: Some theoretical considerations. Psychol. Rev. 70, 80-90,

1963.

R~sum@ :

Quand des sujets doivent nommer une image bri@vement

pr6sent6e, leurs latences de d@nomination sent affect@es si un

mot est pr@sent@ ~ c~t@ de l'image que le sujet soit ou non capa-

ble de reeonnaitre ce mot. Lorsque les mots n'ont pas @t6 identi-

fi@s, l'effet est plus fort avec les mets en relation avec l'image

qu'avec ceux sans relation, mais cet effet est invers@ avec les

mots qui parviennent ~ la conscience. En outre, cette relation d@-

pend fortement de la fonction h6misph@rique gauche. Deux niveaux

d'interf@rence apparaissent dans cette exp@rience : l'effet du aux

mots en relation avec l'image et qui augmente la latence de d@no-

mination et qui se produit ~ un stade pr@-attentionnel du traite-

ment et un effet ult@rieur de comp@tition phon6mique ou articula-

toire qui intervient lorsque l'identit@ du mot @crit parvient

la conscience.

Deutschsprachi~e Zusammenfassun6:

Wenn Versuchspersonen sich der Aufgabe unterziehen, eine kurz

gezeigte Abbildung zu benennen, dann wird ihre Benennungs-

latenzzeit beeinfluSt dureh ein Wort, das sei±lich yon der

Abbildung gezeigt wird tund zwar unabhWngig davon, ob die

Vpn. f~hig sind, das Wort zu erkennen, oder nisht. Werden die

W~rter nicht genannt, so ist die Wirkung bei W~rtern mi% Be-

ziehung (zu der Abb.) starker als bei beziehungslosen. Aber

das Umgekehrte ist der Fall bei W~rtern, die bewuSt werden;

Dardber hinaus ist diese Beziehung weitgehend eine Funktlon

der ILnken Hemisph[re. Zwei !nterferenzebenen werden in diesem

~xperiment offenbar: Die Wirkung der beziehungstragenden ]i~rter,

rile den Benennungsproze$ ve:~zSgern, tritt im Stadium des Auf-

~erksamwerdens ein und eine weitere Auswirkung besteht im

phonemischen oder artikulatorisehen Wettstreit, die sich,

wenn die Identit~t des gedruckten Wortes bewu~t wird, bemerk-

bar macht.