(Coltheart, Laxon, Rickard, & Elton, 1988; Treiman, Freyd, & Baron, 1983). ..... recall (Baddeley, 1990; Morris & Jones, 1990b; Watkins, Watkins, & Crowder, ...
TH E QUARTE R LY JOU RNAL O F E XPE R IM E NTAL PS YCH OL OG Y, 1996, 49A (2), 398± 416
Effects of Irrelevant Soun ds on P hon ological Coding in Readin g C om prehension and S hort-term M em ory Robyn Boyle and Veronika C oltheart M a cqua rie U niversity, S ydney, A ustra lia
T h e effects of irrelevan t so u n d s o n read ing com p reh en sio n an d sh ort-te r m m em ory w ere stu d ied in tw o e xp erim en ts. In E xp erim en t 1, ad u lts jud ged th e accep tability of w ritten se nten ces d u ring irreleven t sp eech , ac com p an ied an d u n accom p an ied sin ging, ins tru m en tal mu sic, an d in silen ce. S en tences varied in sy n tactic com p lexity: S im p le sen ten ce s con tained a righ t-br an ch ing relative clause (The a ppla use plea sed the woma n tha t ga ve the speech) an d sy n tactically com p lex sen ten ces included a cen tre-em bed d ed relative clause (The ha y tha t the fa r mer stored fed the hungry a nima ls). U n accep table sen tences either so u n d ed accep table (The dog cha sed the ca t tha t eight up a ll his food) or d id n ot (The ma n pra ised the child tha t sight up his spina ch). D ecision accu ra cy w as im p aired by sy ntactic com plexity bu t n ot by irrelevan t so u n d s. P ho n ological codin g w as ind icated by increased er ro rs on u n acceptab le senten ces th at so u nd ed cor rect. T he se erro r r ates w ere u n affected by irrelevant so u n d s. E x perim en t 2 exam ined effects of irrelevan t so u n d s on orde red recall of ph o no logically sim ilar an d d issim ilar w ord lists. P h on ological sim ilarity im paired recall. Irrelevan t sp eech red u ced recall bu t did n ot inter act w ith ph on ological sim ilarity. T h e resu lts of th ese exp erim en ts q uestion assu m p tion s abou t th e relation sh ip betw een sp eech inp u t and p ho n ological cod ing in read ing an d th e sh ort-te r m sto re.
T he po ssible role of phonological codes in read ing com prehensio n has b een the subject of investig ation for m any years. D espite considerable evidence for the utilization of phonolog ical codes in short-ter m m em ory, the q uestion as to w hether these cod es are an essen tial com p onent of skilled read ing rem ains unan swered. E viden ce for the activatio n of pho nological codes in read ing com prehensio n has been established by w ord an d sentence read ing tasks using hom ophones (these studies are discussed later). H ow ever
Requ ests for rep rints shou ld be add re sse d to V. Colth eart, Psycho logy D epartm ent, S chool of Behaviou ral Scien ces, M acqu arie U niversity, NS W 2109, Au stralia. E mail: bh_coltheart@ hope.ocs.m q.edu .au We would like to than k Ph ilip Boyle for his patie nt and m eticu lou s re cording of the variou s sp oken an d su ng versio ns of the so ngs, and Greg Cu thbe rtson who m ade the tap e rec ord in gs an d provide d technical assistan c e. We are g rateful to Alan Taylor for his assistan ce w ith ® le conver sion an d comp uting, and to G eorge Coone y for statistic al advice. We than k G. A ltm ann , J. An drade, and S. M o nsell for their edito rial work on the paper. q
1996 The E xp erim ental Psych olog y S ociety
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the function these codes serve in read ing com prehen sion is by no m ean s clear: T hey m ay sim ply be a by-product of au tom atic processing, or they m ay re¯ ect the involvem ent of short-ter m m em ory. Various sug gestions as to p ossible roles short-ter m m em ory m ay p lay in w ritten sentence com prehensio n hav e b een proposed. T hese include the function of m aintaining a verbatim record for sub sequent backtracking (e.g. B add eley & L ew is, 1981; B esner & D avelaar, 1982), or of keeping surface inform ation available w hile the senten ce is parsed (H an so n, G oodall, & Perfetti, 1991 ). A n alter nativ e view is th at a ph onolog ical record m ay be available for assistance during between-sentence integ ration of con cepts an d in for m atio n in text (Coltheart, Avo ns, & Trollope, 1990; S low iacz ek & C lifton, 1980 ). T he view that parsing an d syntactic an alyses m ay be assisted by the m aintenanc e of a pho nological record of the w ords of a sentence w as put forw ard both by psycholingu ists an d by neuropsychologists w ho studied patients w ith short-ter m m em ory an d sentence com prehension de® cits (C aram azza, Ber ndt, & B asili, 1983; C lark & C lark , 1977; Vallar & Bad deley, 1984). M ore recently, how ever, the notion that syntactic an alyses in sentence co m prehension m ake dem an ds on short-ter m w orking m em ory has b een disputed (M artin, 1993; Waters, C ap lan, & H ildeb ran dt, 1987; Vallar & Shallice, 1990). M uch recent research o n sentence com prehension indicates that syntactic an d sem an tic infor m ation is processed o n-line as each w ord is encoun tered (see Rayner, Sereno, M or ris, Schm au d er, & C lifton, 1989, an d M arslen-W ilson , Tyler, War ren, G renier, & L ee, 1992, for a discussio n). It has b een suggested that the involvem ent of short-ter m working m em ory is restricted to the com prehension of long an d com plex sentences (B ad deley, 1986) an d that a ph onological cod e an d the articulatory (pho nological) loop system of short-ter m working m em ory is used at a late stage of sentence processing w hen the output of syntactic an d sem an tic an alyses is com pared to pragm atic an d real world kn ow ledge (Waters et al., 1987). If short-term m em ory is an inte gral com ponent of read ing com prehension, it m ight be expected that tasks know n to interfere w ith sh ort-term m em ory w ill ex ert sim ilar inte rference effects o n th e com prehension process. T he contrib ution of short-ter m m em ory has been stu died usin g a m em ory load , co ncurren t articulation, an d irrelevan t (heard ) speech. Both a m em ory load an d concu rrent articulatio n have been found to im pair the com prehension of lo nger sentences (B ad deley, 1986; Badd eley, E ldridge, & L ew is, 1981; Waters et al., 1987). T he effects of irrelevan t speech on sentence com prehen sion, however, have not been co nclusively established. Ir relevan t sp eech is k now n to im pair serial short-ter m list recall (Colle & Welsh, 1976; Salam e & B add eley, 1987, 1989), re gard less of the m ean ingfulness of the sp eech or the intensity at w h ich it is p resented (B ad deley & Salam e , 1 986; C o lle, 1980; Jones, M iles, & Page, 1990). Further m ore, not all irrelevan t au ditory m aterial interferes w ith serial short-ter m recall: w hite noise, pink noise, au ditory tones, an d hum m ing do not interfere to the sam e extent as does verbal m aterial, if at all (Jones, 1993; M or ris, Jones, & Q uayle, 1989; Salam e & Baddeley, 1982). It has therefore been argued that au ditory verbal m aterial (e.g. speech, singing ) g ains obligatory access to a pho nological sh ort-term store an d interferes w ith the storage of list item s input by th e rehearsal process (B add eley, 1986, 1992; Bad deley, L ew is, & Vallar, 1984). A ccording to th e working m em ory m odel of Bad deley an d H itch (1974; B add eley, 1986), visually presented verb al m aterial is recoded into a pho nological for m an d stored in a pho nological
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sh ort-term store w ithin workin g m em ory. Item s w ithin the store are refreshed by su bvocal reh earsal utilizing the ar ticulatory (pho nological) loop. Interference by irrelevan t aud itory m aterial observed in short-ter m m em ory tasks occurs becau se the au ditory m aterial au tom atically enters the phonological short-ter m store an d cor rupts or replaces item s currently held there (Baddeley, 1990; Salam e & B add eley, 1986). If this pho nological com po nent of short-ter m w orking m em ory is involved in read ing co m prehension, then irrelevan t speech m ight b e expected to interfere w ith the co m prehension process. Few studies have directly exam ined the effects of irrelevan t sounds on read ing com prehension, although interest in the interferen ce of au d itory m aterial w ith read ing ex tends b ack to 1945, w hen H en derson , C rew s, an d B arlow assessed the effects of popular an d classical m usic o n read ing, w ith the aim of deter m in ing w hether studying w ith the rad io on d istracted students from their w ork. T hey foun d that popular m usic reduced parag rap h com prehension, but classical m usic did not. H ow ever, they did not co nsider the fact that in add ition to differing in m usical genre, the popular m usic w as vocal, w hereas the classical m usic w as entirely instrum ental. M ore recently, M artin, Wog alter, an d Fo rlano (1988) assessed m em ory for factual m aterial from text passages read in the p resence of irrelevan t speech an d various other on going sounds. A lthough an y verbal m aterial, w hether spoken or sung, produced adv erse effects o n recall, g reater effects occurred for sp eech in the listener’ s ow n language than for speech in a fo reign or u nfam iliar language. M artin et al. concluded that the irrelevan t speech interfered w ith sema ntic coding rather than phonologica l coding. H owever, their m em ory tests w ere presented after a ® lled delay so as to m inimiz e the contribution of short-ter m working m em ory. C o nsequently, the task re¯ ects the functioning of (long-ter m ) ep isodic m em ory, rather than short-ter m w orking m em ory. Jones et al. (1990) exam ined the effects of various irrelevan t sound co nditions o n a proofreading task. T hey found that sp eech disrupted accurac y in detectin g certain sorts of typog rap hical er rors an d not others. Speci® cally, speech im paired the detection of su per® cial features of the text: letter om issio ns an d m isspelling s. D etection of contextual er rors req uiring com prehension (e.g. inap propriate w ords an d gram m atical errors) w as unaffected by irrelevan t speech. A lim it on the conclusio ns th at can be draw n is that no tests of com prehension followed th e proofread ing task, an d it is p ossible that su bjects were simply skim m ing the text. Becau se of the read ing parad igm s u sed, neither of these previous studies indicates w hether pho nological codin g serves a fun ction durin g read ing com prehensio n or w h ether irrelevan t sp eech affects the for m ation an d/or use of this code. E viden ce for the operation of p honological codes during read ing com prehensio n has existed since B aro n’ s (1973) research on phrase evaluation. Subseq uen t research using longer sentences containing inap propriate hom opho nes has show n that skilled read ers derive pho nological co des during read ing, an d that these codes cau se errors in sentence evaluatio n (Coltheart, L axo n, R ickard, & E lton, 1 988; Treiman , Freyd, & B aro n, 1983). In these ex periments, sentences co ntain ing a hom opho ne, such as The none wa s in church toda y, are er roneously judged as acceptable m ore often than sentences co ntaining an orthog rap hic co ntrol word, such as The nine wa s in church toda y. T his phonological effect on error rate is rem oved by co ncur rent ar ticulation (C oltheart et al., 1990). T hus, phonological codes
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are activated during the read ing of quite sim ple sentences. If such codes are required during the an alysis o f m ore com p lex for m s of syntactic str ucture, th e phonological effects sh ou ld be even g reater w hen dif® cult sentence structures are presented .
E X PE R IM E N T 1 E xperiment 1 investigated phonological coding d uring the read ing of a m ore com plex for m of sentence structure that ad ults ® nd relatively dif® cu lt to co m prehend. T he co m plex sentence structure contained a centre-em bedd ed relative clause (e.g. The mea t tha t the butcher cut delighted the customer) an d it w as contrasted w ith a simp ler stru cture co ntainin g a right-b ranching relative clause (e.g. The ma n hit the la ndlord tha t requested the money). Increased error rates an d RTs have been found for centre-em bedded sentences presented to ad ults, children, an d ap hasic patients (C ap lan , Baker, & D eh au t, 1985; C ook, 1975 ; Waters et al., 1987). A cceptable an d unacceptable sentences of these two types w ere presented in a sentence evaluation task in w hich skilled read ers m ad e speeded judgem ents as to w hether each sentence w as acceptable E nglish, w ith no gram m atical, spelling, or other er rors. T he sim ple an d co m plex unacceptable sen tences w ere of two types: phonolog ically plausible (con taining a hom ophone) or phonologically implausible (containing an orthogr ap hic control w ord). N oun an imacy w as controlled an d b alan ced across b oth acceptable an d unacceptable sentence types, as an imate nouns are typically m ore read ily assum ed to be agents than are inan imate n oun s (C om rie, 1981). T he effects of irrelevan t sounds on read ing com prehension w ere also studied. In m ost previou s research on the effects of irrelevan t so unds, the differences between different classes of sound have not been system atically controlled. W hen instrum ental an d vocal m usic have been contrasted, these have differed in m usical style, num ber an d type of instrum en ts used, an d in m an y other features. C ontrasts b etween speech an d singing have been based on spoken prose an d accom pan ied so ngs d ifferin g g reatly in con tent. T here are m an y possible differences between accom pan ied for m s of song: for exam ple, w h ether one or m o re instru m ents accom pany the singer can g reatly affect the in telligib ility of the words sung b ecau se of the m asking generated by different types an d differing num bers of accom pany ing instrum ents. C on sequently, th e irrelevan t sounds in E xperim ent 1 w ere co nstructed to vary m ore system atically. F ive types of sound conditions were con structed: sp eech, unaccom pan ied singing, accom pan ied singing, instrum ental m usic, an d silence. T he sam e m aterial w as used in the spoken an d various m usical versio ns an d consisted of G ilbert an d Sullivan ``patter’ ’ songs, cho sen for th eir un ifor m ity of m usical characteristics. Patter so ngs attem pt to m imic the continuous ¯ ow ing rhyth m of n or m al speech, do not use the exaggerated vow el so unds found in other so ngs containing lo ng sustained notes, an d do not have large leaps in pitch. T hus, they resem ble speech m ore than do m ost other so ngs. T h ese so ngs w ere also suf® ciently lon g to enable presen tation of soun d seg m ents that w ere not repeatedly played over an d over, thus lessening the likelihood of habituatio n (M orris & Jones, 1990a). U se of this m aterial also m ad e it possible to construct vocal an d instrum ental versio ns of four d ifferent patter so ngs sp oken or sun g by the sam e perfor m er, w ith accom pan im ents played by the sam e m usician. T his bo th en abled presentation of a given song in on ly one ver sion to each su bject an d increased the generality of the ® ndings, w hich were thereby not co n® ned to a sing le so ng.
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T he sentences w ere presen ted along w ith each of th e four sou nd co nditions described above an d also in silence. T h e experim ent used a repeated-m easu res design w ith the order of sound cond ition s an d sentence set counterbalan ced across su bjects. It w as predicted that if irrelevan t speech soun ds (phonem es) have obligatory access to a phonological store used in sentence com prehen sion, then th e vocal sou nd co nditions would disrupt sentence evaluation m ore th an w ould the instrum ental an d silent conditions. If reliance on a phonological code d epends on syntactic com plexity, then the adve rse effects of vocal soun ds m ight b e increased for com plex sentences w hen com pared to sim ple sentences. Finally, if reliance o n phonological coding is m ore likely for syntactically com plex senten ces, then er rors to com plex unacceptable hom ophon e sentences can be predicted to ex ceed those to their simple cou nterp arts. A reduction of these phon ological effects by vocal sound conditions m ight be expected if irrelevan t speech is assum ed to inhibit phonological coding.
M eth o d Subjects Fo rty ® rst-year behaviou ral sciences stu den ts from M acquarie U niver sity participated in the study for course credit. S ubjects ran ged in age from 18 to 54; all reported n or m al hearing an d nor m al or cor recte d-to-norm al vision an d w ere native E nglish speakers. Stim ulu s M aterials and Con ditions S ound B a ckgrounds. T h e backg ro un d so u n d co n ditio ns co ns isted of a silent con tro l co nd itio n an d fou r so u nd con d ition s: (1) instru m en tal m us ic, (2) sin ging w ith instr u m en tal accom p an im ent, (3) u na ccom p anied sin ging, an d (4) sp eech . Fou r G ilber t and S u llivan ``p atter’ ’ so n gs w ere ch osen for the so u n d con dition s becau se of th eir un ifor m ity in ter m s of m u sical style, p itch r ang e, m e lod ic con tou r s, an d rhy th m ic p atter ns. E ach of th ese so n gs w as recorde d in e ach of th e above con dition s, creating fou r versio n s of each so ng : an instru m en tal ver sion , a su n g versio n w ith instru m en tal accom p an im ent, a su n g ver sion w ithou t accom pa nim en t, an d a sp oken versio n . E ach so ng w as ed ited on to a tap e th ree tim es to pro d u ce a con tinuo u s recordin g lasting ap p roxim ately 9 m in. T h is w as d on e in ord er to ens u re th at so u n d s d id n ot cease b efore th e en d of sen ten ce p res entatio n for an y u nu su ally slow su bjects. A train ed bariton e an d m usical com edy p erfo r m er san g an d sp oke th e so n gs for th e recordin gs. T h e sp oke n ve rsio n s of th e so n gs w ere u ttered in a con tinu ou s m ann er at th e sam e sp eed as th e m usical versio n s. T h e rate of u tter an ce w as p aced by a m etron om e ru n n ing at 132 be ats p er m inute, w ith tw o to th ree sy llables per beatÐ ap p rox im ating a no r m al rate for co nv ersa tion al sp eech (an d slow er th an th e 184± 200 beats p er m inu te at w h ich th ese so n gs w ou ld n or m ally be p erfor m ed ). T h is en sure d u n ifor m ity of sp eed s acro ss th e four so n gs an d acro ss th e fou r versio n s of each so n g. T h e sp oken versio n of each so n g h ad th e sam e rhy th m and p au se s as the su n g versio n s. T h e instru m en tal versio n w as p rod u ced by a syn th esized clarinet playing th e m elod y of th e so n gs at th e sam e p itch as that of the vocal co n ditio ns, w ith p iano accom p an im ent. T h e sam e p iano accom p an im ent w as u sed for the accom pa nied sing ing con d ition . Sou n d b ackg ro u n d s w ere played on a M aran tz S u p erScop e tape recorde r (m od el C ± 2 07± L P) an d p resen ted th ro u gh San su i (Typ e S S2) stereo head p h on es at an avera ge level of 75d B(A ). T h is is qu ite lou d, d istr acting, an d d if® cult to ign ore. T h e am b ien t level for th e silen t co nd ition w as 37dB (A ).
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S entence R ea ding Ta sk . T h e stim uli con sisted of 160 acceptab le an d 160 u n accep table sen ten ces 1 d ifferin g in syn tactic com p lexity. H alf th e sen tences of each typ e con tained an anim ate s ub ject (e.g. ma n, girl, dog), an d h alf con tained an inan im ate sub ject (e.g. ta ble, book, house). A ll s enten ces con tained on e of tw o typ es of relative claus e. T h e sy ntactically s im p le s enten ces h ad a righ tbran ch ing relativ e clause m od ifying th e object n ou n p h rase of th e m ain clause (e.g. The a ppla use plea sed the woma n tha t ga v e the speech). T he sy n tactically com p lex sen tences con tained a cen treem bedd ed relative clause in w h ich th e relative clause m od i® es th e su bject n ou n p hr ase an d p reced es the m ain clause verb (e.g. The ha y tha t the fa rmer stored fed the hungr y a nima ls) (Water s et al., 1987). A set of 160 u n accepta ble senten ces w as for m ed by re placing a w ord w ith an inap pro p riate h om oph on e or w ith an or th og rap h ically sim ilar con tr ol w ord . U n accep table h om op h on e sen ten ces w ere p h on ologically p lausible, w hereas u n accep table con tro l sen tences w ere p h on ologically im p laus2 ible. A ll u n acceptab le sen ten ces w ere sy n tactically an d/ or sem an tically an om alou s and h ad been jud ged so by p ilot su bjects. H alf of th e sen tences w ere sy n tactically sim p le an d h alf were com p lex as d escr ibed above. S om e exam p les of th e four sen ten ce typ es follow:
1. 2. 3. 4.
The mother ta ut the child tha t pla yed the cla rinet (sim ple w ith hom ophone); The tea cher tight the cla ss tha t pa inted the poster (sim ple with orth ogr ap hic co ntrol w ord); The truck tha t the boys wa tched toa d a wa y the cra ne (com plex with hom opho ne); The va n tha t the police drove toned a wa y the pa rked ca r (com plex w ith orth og rap hic control word).
Two versio n s of th e un accep table sen tences w ere con str u cted s uch th at in Set 1, Sen ten ces 1 an d 3 con tained the h om op h on e su bstitu tion s, an d in S et 2, S enten ces 2 an d 4 h ad th e h om oph o n e su bs titution s, an d S en ten ces 1 an d 3 h ad th e orth ogr ap h ic co ntro l wo rds. T h e 80 h om oph on es an d th eir or th og rap h ic co ntro ls w ere m atch ed on m ean log wo rd frequ en cy: 1.16 for h om op h on es an d 1.06 for con trols in sim ple sen ten ce s; 1.01 for h om op h on es an d 1.12 for con tr ols in com p lex sen ten ces (Jo h an sso n & H o¯ an d , 1989) an d on m ean g rap h ic sim ilarity: 605, 605, 647, an d 646, resp ectively (Weber, 1970). T h e w ord s are listed in th e A p p end ix. T h e an om alou s h om oph on e or co ntro l wo rd oc cur red equ ally often at th e beginn ing, m idd le, or en d of a senten ce. S enten ces ran ged in len gth from 50± 60 ch ar acter s (9 to 11 w ord s), w ith a m ean len gth of 55 ch aracters.
Procedure E ach sub ject w as tested ind ividu ally in a qu iet ro om . S en tences w ere p resen ted on e at a tim e on a M acintosh com pu ter us ing th e P sych lab p ro g ram m e (G u m & B u b, 1985 ). Su bjects w ere instru cted to read each senten ce silently an d to d ecide w h ether it m ad e sen se an d w as an accep table E ng lish sen ten ce. Su bjects w ere instru cted to resp o nd as qu ickly an d accu r ately as po ssible by p ressing th e ``/ ’ ’ or ``Z ’ ’ ke ys, labelled ``Yes’ ’ an d ``N o’ ’ , resp ectively. Resp on ses eras ed th e se ntenc e fro m th e
1
We than k Gloria Wate rs w ho kin dly provid ed us with the sen tences use d by Waters et al. (1987) . Ap proxim ately a third of the acc eptable sen tences were taken from their set, an d the re main der were devise d by one of us, as were the unacceptable sen tences, wh ich require d in ap propriate homop ho nes and orthog rap hic co ntrol words. 2 App roximate ly half the unacce ptable sen tences containing hom oph on es an d those con taining orthog raph ic contro l word s were both syntac tic ally an d sem antically anom alous; the rem ain der preser ved syn tactic accep tability and were m erely sem an tically in ap propriate .
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screen an d initiated th e n ext sen ten ce after a con stan t interv al of 1500 m sec. P rior to th e exp erim en t, su bjects w ere given 16 pr actice trials in silen ce, con sistin g of sen ten ces ide ntical in sy n tactic stru ctu re to th e exp erim ental trials. Backg ro u n d so u n ds w ere pre sen ted over a set of head p h on es th at su bjects w ore th ro u gh ou t th e experim en t. T h ey w ere instru cted to try to ignore th e backg rou n d so u n d s an d to con cen tr ate o n read ing th e sen ten ces, an d th ey were assu re d th at n o te st of m em ory for th e au d itory m aterial w ou ld follow. E ach sou n d con dition w as p layed for 10 sec p rior to the ® rst trial of each sen tence block, to p reven t any orienting resp on ses to th e so u nd backg ro u nd s fro m interferin g w ith resp on ses on early trials. T h e ord er of so un d con d ition s and senten ce blocks w ithin so u nd c on dition s w as cou n terbalanced u sing a L atin S qu are, s uch that each su bject resp on d ed to all 320 se nten ces an d exp erien ced each so u nd con d ition , bu t n o sub ject saw th e sam e sen tenc e m ore th an o nce. T h e ord er of th e 64 sen ten ces w ithin each block w as ran d om iz ed . A t th e en d of each block of 64 trials, sub jects w ere given a 2-m in break w h ile th e n ext block of trials an d b ackg ro u n d so u n d c asse tte w ere set u p. A lon ger break w as given after th e th ird block. Follow ing com p letion of th e ® fth block of trials, su bjects com p leted a brief sp elling test to ascertain their kno w led ge of th e h om op h on es u sed in th e senten ce trials. T h is w as a p en cil-and -p ap er task in w h ich su bjects w ere requ ired to ® ll in a m iss ing w ord fro m a senten ce by ch oos ing betw een two h om op h on es [e.g. The truck a wa y the cra ne. ( towed/ toa d)] an d th e p osition of th e corre ct h om op ho ne w as r and om iz ed . T h e en tire exp erim en t lasted ap p rox im ately 45 m in.
R esu lts Spelling K now ledge Task T he spelling know led ge task w as designed to establish w hether sub jects w ere acq uain ted w ith the correct spellings of hom o pho nes used in the unacceptable senten ces. T h e overall er ror rate o n this task w as 1.7% , an d 22 of the 40 su bjects m ad e no errors on the task. T his error r ate w as very m uch lower than the er ror rates reported in the sentence evaluation task below. T he only hom opho ne pair to attract m ore than three errors w as ® r/ fur, w hich generated nine errors. T h us the hom oph one error rate in the experimental task can not be attributed to poor spelling know ledge o n the part of the su bjects. Acceptab le Sentences E rror Da ta . M ean percentages of er rors for simple an d com plex acceptable sentences across the ® ve sound conditions are presented in F igure 1. T he er rors o n acceptable sentences were subjected to a 5 3 2 fully repeated -m easures an alysis of variance (AN OVA), w ith ® v e levels of sound condition (speech, singing, singing + instrum ental, instrum en tal, an d quiet) an d two levels of syntactic com plexity (simple an d com plex). A nalyses were perfor m ed both by subjects (rep orted as F 1 ) an d by item s (reported as 3 F 2 ).
3
Because of a w ord -p rocessi ng error, perfor man ce on a few se ntences in som e of the stimu lu s ® les (3 sen tences in all) had to be e xc lu ded, an d the an alyses repo rte d are based on the score s obtain ed after exclu sion of these sen tences.
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FIG . 1. M ean percen tage of errors to sim ple an d com plex acc eptable sen tences across the ® ve backgr oun d soun d con dition s in E xpe rime nt 1.
T he effect of sound co ndition o n decisio n accuracy w as not sign i® can t. E rror rates were signi® can tly g reater for com plex than for simple sen tences, F 1 (1, 39) 5 21.51, p < 0.0 01; F 2 (1, 150) 5 7.09, p < 0.01. Syntactic com plexity interacted sign i® can tly w ith soun d co ndition in th e by-sub jects an alysis, F 1 (4, 156) 5 2.70, p < 0.04, but the interactio n w as unreliable in the by-item s an alysis, F 2 (4, 600) 5 2.33, p < 0.06. T his interactio n arose becau se the difference in accuracy between sim ple an d com plex sentences w as g reater under som e sound co nditions than others. F igure 1 show s that the interactio n w as largely due to the substantial differen ce in accuracy between simple an d com plex sentences in the instrum ental condition as com pared to m uch sm aller differences in the other cond ition s. In the speech an d singin g co nditions the difference between sim ple an d co m plex sentences w as negligible. H ow ever, this interaction w as only m arginally reliable in th e by-item s an alysis an d there w as no coherent patter n to it. R ea ction Time Da ta . M ean RTs to each sentence type across the ® ve sound conditions ap pear in Table 1. S ubjects’ decision tim es to acceptable sentences w ere n ot signi® can tly affected by typ e of background sound. M ean RTs were signi® can tly faster to simple than to com plex sentences, F 1 (1, 39) 5 71.44 , p < 0.001, F 2 (1, 150) 5 18.71, p < 0.001. T he Sound C ond ition 3 C om plexity interaction w as not signi® can t. T hus, none of th e sound backg rounds signi® can tly affected accuracy or speed of judgem ents to acceptable sentences. In con trast, syn tactic com plexity ex erted a large effect o n both accuracy an d speed of judgem ents, w ith simple sen tences being judged faster an d m ore accurately th an com plex se ntences. U nacceptable S entences E rror Da ta . S im ilar an alyses w ere perfor m ed for er rors an d RTs on unacceptable sentences, excep t that hom op hony w as ad ded as a factor: Sentences w ith hom ophones were p honologically p lausible, w hereas those w ith co ntrol w ords w ere not. T he m ean
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BO Y LE A N D CO LTH E A RT TABLE 1 M e an A c c e p ta n c e R T s fo r E v a lu a tio n o f S im p le an d C o m p lex A c c e p ta b le S e n te n c e s A c ro s s the F iv e B ac k g r o u n d S o u n d C o n d itio n s in E x p e rim en t 1
S entence Type Condition
S imple
Complex
Overa ll mea n
quiet instrumental singing + instrumental unaccom panied singing speech
2809 2788 2749 2885 2813
2964 3019 3032 3070 3094
2886 2903 2890 2978 2953
ove rall mean
2809
3036
N ote:
Reaction times ar e given in millisec ond s.
percentage of er rors for each sentence type across the ® ve sound co nditions is presented in Figure 2. T he sound conditions had n o signi® can t effects o n error rates. Signi® can tly m ore er rors were m ad e to sim ple than to com plex sentences (14 .16% an d 11.31 % respectively), F 1 (1, 39) 5 19.73, p < 0.001, bu t this difference w as not signi® can t by item s. T he m ain effect of hom ophony w as also highly sig ni® can t, F 1 (1, 39) 5 49.16, p < 0.001, F 2 (1, 76) 5 21.15, p < 0.001, w ith the percentage of errors to hom op hone sentences m ore than double that to co ntrol sentences (17.19% an d 8.28% , respectively). A m o ng the interactions, only the C om plexity 3 H om ophony interaction w as signi® can t, F 1 (1, 39) 5 11.19, p < 0.005, but ag ain it w as not signi® can t by item s. T his interaction re¯ ected the fact that a signi® can tly larger hom oph one effect (increased error
FIG . 2 . M ean percen tage of errors to sim ple and com plex unacceptable se ntences (con tain in g hom opho nes or orthog raph ic con trol words) across the ® ve backg rou nd sou nd con diton s in Exp erim ent 1.
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rates to hom op hone sentences) occur red for simple than for com plex sentences, t(39) 5 5.4 2, p < 0.01. R ea ction Time Da ta . M ean cor rect rejection RTs for each of the sentence types an d soun d co nditions are show n in Table 2. T he results of A N OVAs indicated that there w as no signi® can t effect of sound con dition on perfor m an ce, nor were the inter actions of soun d condition w ith com plexity or hom op ho ny signi® can t. T here w as a signi® can t m ain effect of com p lexity in the by-subjects an alysis only: Simple sentences w ere rejected faster than w ere com plex sentences, F 1 (1, 39 ) 5 7.47, p < 0.01, F 2 (1, 76) < 1. Sentences w ith inap propriate hom opho nes w ere rejected faster than were senten ces w ith co ntrol w ords, F 1 (1, 39) 5 72.47, p < 0.001, F 2 (1, 76) 5 4 7.04, p < 0.001. N o other effects w ere signi® can t.
D iscussio n T he m ost striking an d unexpected ® nding of E xperiment 1 w as the failure of irrelevan t sp eech an d oth er vocal sounds signi® can tly to imp air read ing com prehension. N either accuracy nor decision tim e in sentence evaluatio n w as adv ersely affected. T his w as particularly sur prising given the subjects’ (an d experimenters’ ) rep orts that the vocal co nditions w ere very d istracting an d dif® cult to ignore. Syntactic com plexity of acceptable sentences did affect both accuracy an d RTs, as it has done in previous research (C ook, 1975; Waters et al., 1987): C entre-em b edded relative clause sentences were m ore dif® cult to com prehend than w ere right-b ranc hing relative clause co nstruction s. A lthou gh there w as a tendency for com plex unaccep table sentences to be rejected m ore accurately than sim ple unacceptable sentences, the differen ce in accuracy w as not signi® can t in the item an alysis, sug gesting it w as the product of a few sentences only.
TABLE 2 M e an R e je ctio n R T s fo r E v alu atio n o f S im p le a n d C o m p lex U n a c c ep tab le S e n ten c e s A c ro s s th e Five B a c k g ro u n d S o u n d C o n d itio n s in E x p e rim e n t 1.
S entence Type S imple
Complex
H omophone
Control
H omophone
Control
Ov era ll mea n
quiet instrum ental singin g + instrumental unacc om pan ied singin g speech
2553 2595 2531 2573 2663
287 9 282 3 278 7 301 0 293 2
2580 2539 2625 2663 2690
293 9 303 2 296 6 305 5 298 7
2738 2747 2727 2825 2818
over all m ean
2583
288 6
2619
299 6
Condition
Note: Reactio n tim es are given in milliseco nds. U naccep table senten ces are th ose con tain ing hom opho nes or or thog rap hic co ntrol words.
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H om oph ony also affected decisio n accuracy. A s in previous research, sub jects m ad e signi® can tly m ore false alar m s to sentences that sound ed right, an d the er ror rates to these sentences w ere com parable in level to those found w ith m uch shorter, single clause 4 sentences (Colthear t et al., 1988, 1990; C oltheart, Avon s, M asterson, & L axon, 1991). T his error rate can not be attributed to im perfect know ledge of the hom op hones used, as the er ror rates on the spelling know ledge test w ere very low (1.7% ) as stated above. It therefore ap pears that a ph onological code is generated, cau sing subjects to accept phonologically plausible hom opho ne sentences er roneously. E arlier it w as suggested that a p honological record m igh t b e m ore likely to be consulted w hen sen tences are syntactically com plex, resist im m ediate o n-line in terpretatio n, an d possibly require back-trackin g. If that w ere the case, it could b e predicted that syntactically com plex sentences containing inap propriate hom ophones w ould be m ore dif® cult to reject, becau se the phon ological code does not discriminate between ap propriate an d inap propriate hom ophon es. T his did not occur: Syntactic com plexity did not reliably affect rejection accuracy w hen sentences w ere unacceptable. T hus, syntactic com plexity did not seem to increase reliance on a phon ological code. C orrect rejections of unacceptable sentences w ere faster for those co ntaining hom ophones than for those co ntain ing orthog rap hic controls. T hat is, despite signi® can tly m ore er rors to phonologically plausible hom op hone sentences, the time taken cor rectly to reject th ese sentences w as signi® can tly less than that for the p honologically im plausible co ntrol sentences. T h is ® n ding has been reported in previous experim ents (C oltheart et al., 1991), w h ere it w as argued that the pho nological representation of the ina ppropria te hom opho ne also activates that of the a ppropria te hom ophone, thus indicating w hich word sh ou ld have been p resent in the sentence an d facilitating th e rejection p rocess. T his does not occur for the control sentences, becau se activation of the or tho grap hic control w ord’ s phonology does not assist in deter m in ing w hat the ap propriate w ord m ight have been; therefore subjects m ay spend time checking alter native interpretations before rejecting the sentence. T his argum ent w as also proposed by D an em an an d Stainton (1991) to account for their ® nding that sub jects in a proofread ing task were m ore likely to cor rect inap propriate hom ophone su bstitutions than orthog rap hic control substitutions. E viden ce sug gesting th at subjects do attem pt to deter m ine w hat the ap propriate word sh ou ld have b een com es from an eye-m ovem ent study (D an em an & Reingold, 1993) in w hich it w as fou nd that initial ® xation time on inap prop riate hom op hones an d orthog rap hic co ntrols w as com parable, an d w as longer th an that on ap propriate hom ophon es; how ever, there were signi® can tly m ore su bsequent ® xations an d reg ressions to inap prop riate orthog rap hic co ntrol words than to in ap propriate hom oph ones. T hese results su ggest that the pho nolog y of the inap propriate hom opho ne cues the ap propriate w ord,
4
E rror rates on unaccep table sentenc es w ith homop ho nes were alm ost id entical for se ntences in wh ich the hom op hon e was syn tactically as well as sem an tically an om alou s (18% on sem antic ally anom alou s se ntences an d 16% on se m antic ally and syn tactically anom alous sen tences). This su ggests that su bjects did not me rely base their decision on a su per® c ial gramm aticality ju dgeme nt of the syn tactic accep tability of the sen tence. The phon ology of the inapp rop riate w ord in ¯ uenced su bje cts’ decisio ns re g ard less of its syn tactic acc eptabili ty.
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facilitatin g the process of correction in the proofread ing task (D an em an & Stainton, 1 991) an d rejection in the sentence judgem ent task. T he derivatio n of a phonological code in this sentence read ing task w as un affected by co ncurren t irrelevan t sp eech or singing. T hus, if irrelevan t speech sounds (phon em es) g ain obligatory access to a ph onological short-ter m store an d cor rupt or rep lace its co ntents, this store m ay not contribute to the com prehensio n of the types of relative clause structures presented in E xperiment 1 . H owever, it is possible that the sounds used in E xperim ent 1 w ere in effective in interfering w ith pho nological workin g m em ory, even though sub jects found them intrusive an d hard to ignore. T his possibility w as exam ined in E xperiment 2 in w hich the sam e sounds w ere presented during a short-ter m m em ory task.
E X PE R IM E N T 2 A s m entioned earlier, previous research has show n that irrelevan t speech an d vocal m usic impair short-ter m serial recall of visually presented lists of num bers or letters (see B add eley, 198 6, 1990 for review s). A dditionally, studies have exam ined the effects of irrelevan t sounds on the phonological similarity effect in ordered list recall (Colle & Welsh, 1976; Salam e & B add eley, 1986). T he phon ological similarity effect refers to the ® nding that recall of pho nologically similar lists of visually presented w ords or letters is inferior to recall of pho nolog ically dissimilar lists (B ad deley, 1966 ; C onrad & H ull, 1964). C olle an d Welsh (19 76) m an ipu lated p honological similarity u sing lists of eight consonan ts an d exam in ed the effects of irrelevan t speech on ordered recall. T hey found a pho nological sim ilarity effect in silence an d an increased error rate but no sim ilarity effect w ith irrelevan t speech, su ggesting that the irrelevan t speech had abolished the pho nological sim ilarity effect. Salam e an d B add eley (1986) investigated the effects of phonological sim ilarity an d irrelevan t speech o n ordered recall of conso nan t lists varying in len gth from 5 to 8 letters. T hey found that irrelevan t speech impaired recall at all list len gth s, an d that a pho nological similarity effect occurred only for list lengths 5 to 7. T his pho nological similarity effect w as not abolished by irrelevan t speech. T hus, the evidence for the effects of irrelevan t speech on phonolog ical coding is con ¯ icting. C onseq uen tly, Experim ent 2 w as designed to provide fu rther evidence about the effects o f irrelevan t sounds o n phonological coding in short-ter m m em ory. Bad deley’ s (1966) p honologically sim ilar an d dissim ilar 5-word lists were used. Recall of th ese lists has yielded eviden ce of a strong phonological sim ilarity effect in norm al silent co nditions (B ad deley, 1966; C oltheart, 1993), an d this effect is abolished by concur rent articulatio n (Coltheart, 1993). T he four sound co nditions from E xperiment 1 were ag ain presented, along w ith a silent con trol co ndition. T hus, E xperiment 2 investigated w hether the irrelevan t speech, singing, an d music p resented in E xperiment 1 w ere cap able of disrupting ordered short-ter m recall of word lists, an d w hether irrelevan t sp eech an d singing interfered w ith p honological sim ilarity.
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M eth o d Subjects T h irty-® ve ® rst-ye ar B eh aviou r al Scien ces stu d en ts ran ging in age fro m 18 to 52 p ar ticipated in the s tu dy for cou rse cred it. A ll rep orted n or m al h earin g an d no r m al or corr ected -to -n or m al vision , an d all w ere n ative E n glish spe aker s.
Stim ulu s Tasks and Cond itions T h e m em ory task s co nsiste d of 25 p h on ologically sim ilar an d 25 p h on ologically d iss im ilar lists of 5 w ord s each . T h e lists w ere con str u cted fro m a set of 10 sim ilar w ord s (ma d, ma t, ma n, ma p, ma x, ca d, ca t, ca n, ca p, ca b) an d a set of 10 d issim ilar w ord s (cow, da y, ba r, few, hot, pen, sup, pit, rig, bun) u sed by B ad deley (1966, E xp erim en t 3). N o w ord app eared m ore th an on ce in a list, an d w ord s occur red equ ally often in the 25 lists. T h e ® ve so u n d backg rou nd s fr om E xp erim en t 1 w ere use d , n am ely: (1) a qu iet (con tro l) con d ition , (2) instru m en tal m usic, (3) sing ing w ith instru m en tal accom p an im en t, (4) u n accom p an ied sing ing, an d (5) con tinuo u s sp eech . W ithin each of th e ® ve so u n d con d ition s, su bjects w ere p resen ted w ith ® ve sim ilar an d ® ve dissim ilar lists in ran d om ord er. O rd er of p resen tatio n of so u n d backgr ou n d s an d lists w ithin so u n d backgro u n d s w as cou n terb alanced .
App aratus and Procedure E ach sub ject w as tested individu ally in a sin gle sessio n , w ith a 1- m in break betw een each so u n d con d ition an d th e next. A s in E xp erim en t 1, sub jects w ore head p h on es thro u gh w h ich th e so u n d backgr ou n d s w ere p resen ted at ap p rox im ately 75 d B (A ). S ub jects w ere instr ucted to ign or e any backgr ou n d so u n ds th ey m igh t hear an d w ere reassu red th at th ere wo u ld be n o test of th eir m em or y for th e au d itory m aterial. T h e so u n d p resen tatio n beg an 10 sec before th e ® r st list in each block, as in E xp erim ent 1. T h e wo rd lists w ere p resen ted on an IBM p ers on al com p uter u sin g D m astr so ftw are (Forste r & For ster, 1990) p ro g ram m ed to p resen t sim ilar an d d issim ilar lists in a d ifferen t r an do m orde r to each su bject. E ach list w as p reced ed by a 1-se c ® xation p oint, after w h ich w ord s were p resen ted su ccessively in th e cen tre of th e screen for 1 s ec, each im m ed iately rep lacing th e p reviou s w ord. Im m ed iate w ritten recall w as requ ired after every list, u sin g a p rov ided booklet. E ach p age in th e b ooklet con tained a colum n nu m bered fro m 1 to 5, and su bjects w ro te each w ord n ext to the n um b er corre sp on d ing to its serial po sitio n in th e list. It w as em ph asiz ed th at o nly w ord s recalled in th eir corre ct serial p osition w ou ld be scored as cor rect. Follow ing rec all, su bjects initiated p resen tation of the next list. F ive p ractice trials in silen ce p reced ed th e exp erim ental trials.
R esu lts T he m ean p ercen tages of w ords cor rectly recalled in sim ilar an d dissim ilar lists across the ® ve sound co nditions ap pear in F igure 3. A two-factor repeated-m easures A N OVA yielded the following results. Recall of pho nologically similar lists (48.6% ) w as significan tly worse than re call of dissimilar lists (73.3% ), F(1, 34) 5 191.0 0, p < 0.0001. T he m ain effect of sound w as also h ighly sign i® can t, F(14, 136) 5 7.85, p < 0.001. Planned co m parisons u sing the B onferroni procedure show ed that the vocal co nditions imp aired recall w hen com pared to silence, t(136) > 4.0, p < 0.001 for each com parison, w hereas
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instrum en tal m usic did not. Recall in the instrum ental co ndition showed a tendency to be better than recall in any of the vocal conditions, but these com pariso ns just failed to reach signi® can ce. T he Pho nological S im ilarity 3 Sound C on dition interaction w as not signi® can t, p > 0.1. T hus, the phonological similarity effect w as present in all ® ve soun d co nditions. It has been sug gested that the phonological similarity an d irrelevan t speech effects in sh ort-term m em ory tasks arise only w hen both item a nd order in for m ation are required at recall (Bad deley, 1990; M orris & Jones, 1990b; Watkins, Watkins, & C row der, 1974). T herefore an other m eth od of scoring w as ap plied, w herein a w ord w as co unted as co rrectly recalled reg ardless of w hether it w as recalled in its cor rect serial position. It sh ou ld be noted, how ever, that this second scoring procedure can not b e equated w ith free recall as the task required of sub jects w as serial recall. T he m ean percentage of cor rect recall for sim ilar an d dissimilar lists across the ® ve soun d con ditions ap pears in Figure 4. C om parison of m ean s w ith those using the serial recall scoring m ethod show s that overall recall is higher w hen serial order is disreg arded. A repeated-m easures A N OVA show ed the m ain effect of phon ological similarity to be highly signi® can t, F(1, 34) 5 130.49, p < 0.0001, w ith recall of sim ilar lists (67.3% ) signi® can tly w orse th an recall of dissim ilar lists (81.9% ). T h e m ain effect of soun d co ndition w as on ce again highly signi® can t, F(4, 136) 5 5.00, p < 0.001. H owever, these m ain effects m ust be interpreted in the light of the signi® can t Ph onological Similarity 3 Sound C on dition interaction , F(4, 136) 5 3.58, p < 0 .01. F irst, it m ust b e noted that recall of pho nologically similar lists w as signi® can tly worse than recall of dissimilar lists in every sound co ndition, t(170) > 5.00, p < 0.001 in every case. T he interactio n arises becau se of the g reater effect of sound o n the dissimilar than o n the similar lists. Planned com parison s showed th at perfor m an ce on the sim ilar lists did not differ significan tly across the ® ve sound co nditions. Fo r the dissimilar lists, perfor m an ce w as w orse in soun d than in quiet. T he follow ing com p arisons w ere signi® can t: quiet versus singing+ instrum ental; quiet versus singing; quiet versus speech; an d instrum ental versus singing, t(272) > 2.83, p < 0.05 in each case. T hus, although the phonological sim ilarity
FIG . 3. M ean percen tage of correc t recall (correct serial position ) for phono logically sim ilar an d dissim ilar word lists across the ® ve backgr ou nd soun d c ond ition s in Exp erim ent 2.
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FIG . 4. M ean perce ntage of c orrect recall (serial positio n disreg arded ) for phonolog ically sim ilar an d dissim ilar word lists across the ® ve backgr ou nd soun d c ond ition s in Exp erim ent 2.
effect w as signi® can t across all sound conditions, the m agnitude of the effect w as reduced in th e vocal con ditions.
D iscussio n T he results of E xperim ent 2 show ed conclusively th at the irrelevan t sound co nditions presented in E xperim ent 1 w ere effective in red ucing ordered recall in short-ter m m em ory tasks. T his extends the irrelevan t speech effect to sub-span lists of word s (in add ition to lists of digits or letters). Fu rther m ore, it ap pears that vocal sou nds interfered m ore stron gly w ith recall than did instrum en tal m usic, w hich did not greatly reduce recall. D ifferences am ong the various vocal conditions (speech, unacco m pan ied an d accom pan ied singing) were slight an d n ot signi® can t. T h is co n® r m s the resu lts obtained by Salam e an d Badd eley (1989) an d supports the view that som e property speci® c to au ditory verbal m aterial allow s it to g ain access to the pho nological com pon ent of working m em ory. In accord w ith previous research, pho nological similarity of list item s impaired recall. H owever, as in Salam e an d Bad deley (1986), this phonological similarity effect w as m aintained in all the sound co nditions, suggesting that irrelevan t vocal sounds do not preven t ph onological recoding of visually presented w ords an d prob ably do not prevent rehearsal. W hen recall w as scored w ithout reg ard to order, the vocal conditions (com pared to quiet) w ere found to reduce (but not abolish) the effect of pho nolog ical sim ilarity, an d the overall level of recall w as higher. T his suggests that rather th an having been cor rupted or replaced, list item s are in fact retained, albeit in the w ro ng order. T his in tur n im plies that the effect of irrelevan t speech is not one of preven ting or interfering w ith encoding of item s in the phonological short-ter m store or replacing item s currently held there (S alam e & Badd eley, 1986), but, rather, is one of interfering w ith the m aintenan ce of item order infor m ation (see also Jo nes, 1993; Jo nes & M or ris, 1 992). T his suggestion is su pp orted by the ® ndings of Salam e an d Badd eley (1990) that irrelevan t sp eech disrupted serial but n ot free short-ter m recall of a list of word s, an d by M orris an d Jones (1990b),
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w ho found it w as only the serial com po nent of a short-ter m m em ory list recall task that w as susceptible to interference by irrelevan t sp eech.
C O N C LU S IO N S E xperiment 1 exam ined the effects of various irrelevan t vocal sounds (sp eech, accom pan ied an d unaccom pan ied singing) an d instrum ental music o n read ing com prehensio n of two-clau se sentences d iffering in syntactic com plexity. T he contribution of pho nological co ding to read ing com p rehensio n w as assessed by the inclusion of u nacceptable sentences that w ere either pho nologically plausible (containing inap propriate hom ophones) or phonologically im plau sible (containing orthog rap hic controls). Ir relevan t sounds d id not reliably im pair sentence com prehension perfor m an ce; how ever, syntactic com plexity an d phonology d id affect perfor m an ce. Sente nces w ith com plex structure w ere m ore dif® cu lt to com prehend, but there w as no indication th at syntactic com plexity provoked a g reater reliance on the pho nological representatio n of a sentence. T his is co nsisten t w ith Waters et al. (1987 ), w ho found that con cur rent articulation did not interfere w ith co m plex sen tences to a g reater exten t than w ith sim ple sentences. E vidence of the d erivation of a ph onological cod e during sentence read ing w as m an ifest in an incre ase in error rates o n unacceptable hom ophone sentences that sounded acceptable. T he derivatio n of this phonological code w as unaffected by the presence of irrelevan t vocal sounds. Failure to ® nd adv erse effects o f irrelevan t speech an d sin ging o n read ing com prehension w as not due to an inability of the sounds to affect cogn itive processes in general, an d phonological w orking m em ory in particular. In E xperim ent 2, the sam e sound co nditions were presented co ncur rently w ith a short-term m em ory task . Irrelevan t vocal sounds, b ut not instrum ental m usic, im paired ordered recall of 5-w ord lists. S im ilar effects have been reported for th ese sorts of sounds o n ordered recall of digit an d letter lists (e.g. Salam e & Bad deley, 1989). Phonological sim ilarity of list item s also im paired recall, an d this effect w as present under all the co ncur rent sound con ditions. T hus, in both E xperim ents 1 an d 2, pho nological codin g of visually presen ted w ords seem s to b e possible in the presence of irrelevan t vocal sounds. T hese ® ndings r aise questions ab out the view that speech in put g ains obligatory, au tom atic access to a phonological short-ter m store an d that it occup ies slots in that store or replaces infor m ation currently stored th ere. Rather than interfering w ith th e item s them selves or preventing their storage w ithin the p honological store, the sp eci® c effect of irrelevan t vocal sou nds would ap pear to b e on the ability to m aintain item order infor m ation. If this is the case, the seem ingly pu zzling ® nding of clear pho nological (hom ophone) effects w ith out an y correspo ndin g interference by irrelevan t speech m ay be ex plained: A n interference effect m ay o nly be observed w hen the task requires the retention of exact serial order of item s in w orking m em ory. Pre sum ably, only the shortter m m em ory task m ad e this dem an d. A ® nal point of interest is that co ncu rrent articu lation has been found to rem ove phonological (h om ophone) effects in sentence read ing (Coltheart et al., 1990), w hereas in th is study irrelevan t speech failed to do so. T hese differences between the effects of irrelevan t speech sounds an d concur rent articulation can be explained by M onsell’s (1987) m odel. M onsell proposed that the functions of the ``ph onological loop’ ’ are car ried out by recirculating infor m atio n between the two sub-lexical phon ological buffer
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stores, one in th e speech input processing p ath w ay an d one in the speech output processing pathw ay. T he generation of irrelevan t speech by the sub ject interferes w ith both the prod uction of pho nological codes for the list item s an d their m aintain an ce by rehearsal. Irrelevan t speech heard by the su bject interferes w ith the retention of pho nological codes in the in put buffer bu t does not impede the orthograp hical-to-phonological conversio n process, or the imm ediate activatio n of m ean ing by its ou tput. O f course, it is likely that irrelevan t vocal sou nds have other effects, an d M artin et al.’s (1988) research indicated that th e sem an tic content of irrelevan t speech reduced the retention of factual infor m atio n from prose passages. It is also possible that the com prehension of m aterial requiring m ore ex tensive backtracking than the types of senten ces used in this experim ent (such as g arden -path sentences) m ight b e adv ersely affected by irrelevant vocal soun ds, but this rem ains to be investigated.
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A PP EN DIX S IM PL E
CO M PL E X
SIM P LE
CO M PL E X
H omop ho ne
C ontrol
H om oph one
Co ntrol
H om oph on e
C ontrol
H omop ho ne
Co ntrol
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