A systematic review and meta-analysis of dichotic deficits in individuals with learning disability

Figures & data

Figure 1. Prisma flow chart explaining stages of meta-analysis.

Table 1. Summary of evidence from the systematic review.

Sl. No	Title/Author/Year	Participants characteristic (groups, sample size and mean age)	Dichotic test used	Transducer used and stimulus intensity	Responses	Conditions	Findings
1.	Hugdhal (2003)	CG-23 (20B & 3G) Dys G-23 (19B & 4G) MA; - Age range; 10–12 yrs	DCV 6 CV syllables /ba/, /da/, /ga/, /ka/, /pa/, /ta/ Total stimuli; 108 Controlled duration: yes	Intensity – 75 dB SPL	Verbal	FR and DA	Reduced right ear scores in Dys group
2.	Kołtuska, B & Grabowska, A (1992)	CG: 12 (7B & 5G) Dys G: 29 -phonetic disorder: 17 (10B & 7G) Language disorder: 11 (6B & 5G) MA: na Age range: 8–9 years	Exp 1: Two pairs of words separated by 500 ms interval (108 pairs) Controlled duration: NA Exp 2: One pair of two different words (114 pairs)	Conversational level lower than conversational level	Verbal	FR	Significantly higher scores for right ear in all three groups Mean recognition level for both ears was lesser for dyslexics group
3.	Brunswick, N & Rippon, G (1994)	CG: 15 (B) MA: 8.78 ± 0.95 Dys G: 15 (B) MA: 8.87 ± 1.41	DCV Controlled duration: NA 32 dichotic pairs 320 ms duration	Intensity – 75 dBSPL	verbal	FR	Weaker right ear performance by dys group No difference in left ear performance between groups
4.	Caplan, B., & Kinsbourne, M. (1982)	Control group: 40 (21B & 19G) MA – 9.26 ± 1.41 Poor readers: 40 (36B & 4G) MA – 13.39 ± 2.24	DCV CV syllables /ba/,/da/,/ga/,/ka/,pa/,/ta/ ISI, 4msec	Intensity: 50 dBSPL	verbal	FR	No significant degree of dichotic ear asymmetry between the groups
5.	Dermody, P., Mackie, K., & Katsch, R. (1983)	CG: 15 MA – 11.5 years LD group: 15 MA – 12.7 years Gender Information: NA	DCV /pa, ta, ka, ba, da, ga/ 90 msec	Intensity: 80 dB SPL	verbal	FR	No right ear advantage in both groups Differences for the groups are observed only in double-correct responses.
6.	Hakvoort, B., de Bree, E., van der Leij, A., Maassen, B., van Setten, E., Maurits, N., & van Zuijen, T. L. (2016)	CG: 26 DD; FRND: 26 FRD: 17	Dichotic digit test Grade 3 (3 monosyllabic digits /ear) Dichotic listening test Grade 6 (/bɑ/, /dɑ/, /ɡɑ/, /pɑ/, /tɑ/ and /kɑ/)	70 dB 80dB Duration controlled: yes	Verbal	FR & DA	Right ear is dominant FRD group; lower left ear scores show lager REA
7.	Harel, S., & Nachson, I. (1997)	CG: 63 Poor readers: 60 MA: na Age range: 8.9 -12.9 yrs	Pairs of tonal stimulus sets (64 pairs) – three successive high- or low-frequency tones Duration: 600 msec Duration controlled: yes	Intensity: NA	Verbal	FR & DA	Correct responses were highest in free recall and directed attention along with presence of continuous tone in the unattended ear
8.	Helland, T., & Asbjørnsen, A. (2001)	CG: 20 (16B & 4G) MA: 12.11 ± 0.36 Dys G: 43 (36B & 7G) MA: 12.67 ± 1.68	CV syllables (108) Duration controlled: NA	Intensity: NA	Verbal	FR&DA	Weak left ear dominance in dys group and that of right ear in CG
9.	Asbjørnsen, A. E., & Helland, T. (2006)	CG: 20 MA: 12.11 ± 0.36 LD group: 43 (RI/NLI – 25 RI/LI – 18) MA: 12.67 ± 1.68	DCV CV syllables /ba/,/da/,/ga/,/ka/,pa/,/ta/ Duration controlled: no	Intensity: NA	Verbal	FR&DA	Reduced left hemisphere language dominance with reading impairment
10.	Kershner, J., & Micallef, J. (1991)	CG: 30 (boys) MA: 7.8 ± 0.9 LD group: 30 (boys) MA: 11.3 ± 1.1	DDT 350msec duration Duration controlled: NA	> 70dB	Verbal	DA	Equal number of subjects showed REA in both groups
11.	Helland, T., Asbjørnsen, A. E., Hushovd, A. E., & Hugdahl, K. (2008)	Control group: 40 (29B & 11G) MA: 12.40 ± 0.58 Dys group, D1: 20 (10B & 10G) MA: 12.86 ± 0.65 D2: 20 (14B & 6G) MA: 12.59 ± 0.92)	DCV syllables	Intensity: NA	Verbal	FR	-Significantly more correct responses from the right ear -REA was absent in the D2 group compared to D1 and CG
12.	Hugdahl, K., Heiervang, E., Nordby, H., Smievoll, A. I., Steinmetz, H., Stevenson, J., & Lund, A. (1998)	Control group: 25 (Mean age 11.7 ± 0.5) Dyslexic group: 25 (Mean age 11.8 ± 0.4)	CV syllables /ba/,/da/,/ga/,/ka/,pa/,/ta/ 36 dichotic pairs and 36 trials Duration: 400msec	(75 dB)	verbal	FR&DA	Significant REA in both groups during DA (R) and no significant for DA (L)
13.	Hynd, G. W., Obrzut, J. E., Weed, W., & Hynd, C. R. (1979)	CG: 48 (40B & 8G) LD group: 48 (40B & 8G) younger group of 24 children MA: 8.3 ± 8.19 24 older children MA: 10.6 ± 7.46	DCV 30 pairs Controlled duration: NO	55 dBHL	verbal	FR	Significant RE effect in both the groups
14.	Hynd, G. W., & Obrzut, J. E. (1981)	(3 groups of 30) CG: 15 LD group: 15 Younger group, MA: 8 ± 4.78 Intermediate group: 9.5 ± 6.56 Oder group: 11 ± 5.12	DCV 30 pairs- /ba/ ka/da/ga/ta/pa/ Controlled duration: NO	Intensity: NA	verbal	FR	Significant RE effect in both groups
15.	Kershner, J., Henninger, P., & Cooke, W. (1984)	Exp: 1 CG: 15 (B) Dys group: 15 (B) MA: na Age range: 10–12 yrs	84 dichotic pairs of monosyllabic digits (36 trails) single, double, triple, and quadruple pairs duration: 306msec Controlled duration: NA	70 ± 5 dBHL	Written and verbal	FR	Significant REA for CG Dys group produced a significant LEA The dys-phonetic children showed RH (hemisphere)A when responding in writing, condition
16.	Kershner, J. R., & Morton, L. L. (1990)	Exp:1 CG: 32 (27B & 5G) MA: 12.0 ± 1.0 LD group: 32 (27B & 5G) MA: 12.3 ± 1.4 Exp:2 Control group: 14 LD group:14	-64 dichotic pairs of monosyllable digits -two blocks (8 trials each) of quadruple pairs Duration: 307msec	65 dBHL	Written and Verbal	FR&DA	LD group-maintained REA in the right-first condition. (both exp)
17.	Kershner, J., & Micallef, J. (1991)	CG: 34 Dys group: 12 MA = 10.8 ± 1.2	350-msec duration 64 dichotic pairs of monosyllable digits duration controlled: NA	70 dBHL	Verbal	FR	Reading condition, greater REA in all three groups
18.	Kershner, J., & Micallef, J. (1992).	CG: 30 MA: 11.6 ± 1.1 DyS group: 30 MA: 11.3 ± 1.1	Dichotic CV Syllables quasi-random arrangement duration controlled: NA	70 dBHL	Verbal	FR&DA	Superior talents in LE recall which implicates a right hemisphere skill in dys group
19.	Keefe, B., & Swinney, D. (1979)	CG: 19 DD group: 19 MA: 10.0 yrs	Dichotic digits 2 digits pair per second Duration controlled: yes	Intensity – NA	Pointing	DA	RE superiority by both groups
20.	Kershner, J. R. (2016)	CG: 34 (6B & 28G) MA: 33.5 ± 9.3 Dys group: 73 Mod group: 42 (21B & 21G) MA: 26 ± 6.5 Sev group: 31 (19B & 12G) MA: 27.2 ± 7.9	Dichotic CV Syllables Duration controlled: yes	70 dBHL	Written	DA	LF, significantly greater REA by CG compared to mod group RF, lower REA by CG compared to sev group Poorer ability to shift from right to left
21.	Koomar, J. A., & Cermak, S. A. (1981)	CG: 30 (23B & 7G) MA: 9.0 yrs LD group: 30 (23B & 7G) MA: 8.10 yrs	DCV syllables DDT (20 series of 3 pairs of digits) Duration controlled: NA	74 dBSPL	Verbal	FR	Similar scores for LD group and CG on CV but significantly lower than the normal group on the digts
22.	Gupta, Pradip kumar (2015)	CG: 10 (9B & 1G) Dys group: 10 (7B & 3G) MA: na Age range: 10–12 yrs	DCV syllables Duration controlled: yes	40 dB SL	Verbal	FR & DA	Dys group: LEA observed Poorer performance on DCV test for single correct score of right ears, left ear and of double correct scores
23.	Martínez, J. A., & Sánchez, E. (1999)	CG: 75 (B) (age matched: 50 Reading level matched: 25) MA: 9.93 ± 0.72 Dys group: 50 (B) MA: 10.24 ± 0.84	DCV syllables Duration controlled: no	Intensity: NA	verbal	FR&DA	No significant differences were found for the FR and DA
24.	McKeever, W. F., & VanDeventer, A. D. (1975)	CG: 9 MA: 13.7 Dys group: 9 MA: 13.9	DDT 3 pairs	Intensity: NA		FR	LD possess left hemisphere language specialization and clear auditory memory deficits
25.	Menashe, S. (2019)	CG: 22 (11B & 11G) MA: 25.4 ± 3.35 Dys group: 18,(9B & 9G) MA: 26.4 ± 4.37	Dichotic CV syllables, Duration: 380ms Dichotic Vowels Task, 200 dichotic Vowels, 320ms	75dBHL	Pressing the button	DA	Differently organized auditory system with altered speech lateralization in adult dyslexic readers
26.	Moncrieff, D. W., & Black, J. R. (2008)	CG: 10 (7B&3G) MA: 11.8 ± 0.4 Dysc group: 10 (7B&3G) MA: 11.6 ± 0.3	DDT DCV Competing word subtest (50 pairs of single syllables words)	50 dB SL Duration controlled: NA	verbal	FR&DA	67%dys children showed clinically significant left ear weaknesses on DDT-FR Reduced right ear performance with CVs has been reported for children with dyslexia
27.	Morton, L. L. (1994)	CG: 20 (B) RD group: 40 (B) (4 subtypes) MA: na Age range: 9–12 years	Dichotic CV syllables, mixed order Duration controlled: no	70 dBHL	Verbal	FR&DA	RD group showed stronger REA on bilabials compared to alveolars and velars
28.	Milberg, V. W., Whitman, R. D., & Galpin, R. (1981)	CG:12 (B) MA: 10.0 yrs LD group: 12 (B) MA: 9.8years	Dichotic digit test -One digit of each pair Duration controlled: NA	Intensity: NA	Verbal	FR	Left ear yielded fewer errors than the right ear when it was the stored channel.
29.	Swanson, H. L. (1987)	CG: 16 (8B & 8G) MA-11.52 ± 0.94 LD group: 16 (8B & 8G) MA- 11.85 ± 0.69	Dichotic words (12 mono-syllabic or Bi-syllabic pairs) Duration Controlled: Yes	60 dB HTL	verbal	FR& cued recall	Recall was significantly higher for words in the LE than in the RE CG, immediately available for recall than LD group, irrespective of word feature
30.	Swanson, H. L., & Mullen, R. C. (1983)	CG: 24 (B) MA:11.63 ± 0.68 LD group: 24 (B) -older LD, MA: 12.2 ± 0.24 -younger LD, MA:8.75 ± 1.30	Nine words lists (3 semantic, 3 phonemic, 3 unrelated) in competing noise -12 monosyllable words Duration Controlled: Yes	60 dB HTL S/N ratio: 10	Verbal	FR&DA	LD group recalled more words on the both ear (left ear than right ear) LD group prefers semantically organized words in the LE, REA for phonemically organized and unrelated word lists for the older age.
31.	Pinheiro, F. H., Oliveira, A. M. D., Cardoso, A. C. V., & Capellini, S. A. (2010)	CG: 20 LD group: 20 MA: na Age range: 8–12 years	DDT (20 digits pairs, 4 digits to both ears) Portuguese-Language Alternate Dissyllable Dichotic test (SSW)	50 dB SL	verbal	FR&DA	Mean performance of LD group was lower than CG (both ears)
32.	Patel, T. K., & Licht, R. (2000)	CG: 20 (B) MA: 10.87 LD group; 33 (27B & 6G) P dyslexics: 14 MA: 10.38 yrs L dyslexics: 19 MA: 11.45 yrs	2 syllable Dutch words, four different affective tones, 144 pairs Duration controlled- yes	Normal speech loudness	Button press	FR	No significant ear advantage for P-types, and a REA for L-types and controls
33.	Obrzut, J. E., Bryden, M. P., Lange, P., & Bulman-Fleming, M. B. (2001)	CG: 72 (12B & 12G/grade) I, MA: 6.3 yrs III, MA: 8.2 yrs V, MA: 10.3 yrs LD group: 30 Age range: 8.0–11.10 yrs	2 syllable words, four different emotional tones, 144 stimulus pairs Duration controlled – yes	-	Verbal	FR	LD group, better RE scores than LE for words target
34.	Aylward, E. H. (1984)	CG: 34 LD group: 72 Dys-eidectics: 20 Dys-phonetics: 12 Non-specific dys: 20 MA: na Age range: 7–12 yrs	DDT 2 digits pair per second, 10 sec pause b/w trials	Constant volume	verbal	DA	Significant REA exhibited by dys-phonetics group, but not by CG and dys-eidetics group
35.	Beaumont, J. G., Thomson, M., & Rugg, M. (1981)	CG: 26 (B) MA (in months): 118.6 ± 10.2 LD group: 26 (B) MA: 118.6 ± 10.4	DDT Duration controlled: yes	Intensity: NA	Verbal	FR	Both groups showed a REA, and there was no overall difference between the groups in performance
36.	Obrzut, J. E., Obrzut, A., Bryden, M. P., & Bartels, S. G. (1985).	CG: 16 (14B & 2G) LD group: 16 (14B & 2G) MA: na Age range: 7.8–12.1 yrs	DCV syllables (30 Pairs)	55dBSPL	verbal	FR&DA	Greater dichotic recall for CG LD group, no consistent REA More correct responses from LE for DA (L)
37.	Bowen, S. M., & Hynd, G. W. (1988).	CG: 24 (17B & 7G) MA: 21.98 yrs LD group: 24 (17B & 7G) MA: 22.07 yrs	DCV syllables, Dichotic words, Dichotic sentences, Duration controlled: NA	Intensity: NA	Verbal	FR&DA	Both groups, REA present Most accurate responses for D words and DCV had least accurate scores DA(R) most correct responses
38.	Obrzut, J. E. (1979)	CG: II:19 IV: 27 Non-specific: II: 10 IV: 8 Dys group: (Dysphonetic Dyseidetic, Alexic) II: 43 IV: 37	DDT Duration controlled: yes	60 dB SPL	-	FR&DA	CG and dys-eidetic group showed better recall than dys-phonetic & alexic group significant REA only for dys-phonetic
39.	Obrzut, J. E., Conrad, P. F., Bryden, M. P., & Boliek, C. A. (1988).	CG: 15(10B & 5G) LD group: 15(8B &7G) LH group: 15(9B & 6G) Bilingual children: 15(8B &7G) MA: 9.9 yrs	DCV syllables, 3 sets and 30 trails Duration controlled: yes	55 dB SPL	Verbal	FR&DA	Constant REA by CG for all conditions LD group, REA for FR and DA(R) No ear differences for DA(L)
40.	Obrzut, J. E., Conrad, P. F., & Boliek, C. A. (1989)	CG:30(1B & 19G) LD group: 30(20B &10G) MA: 10.5 ± 1.8	DCV syllables non-verbal stimuli (serial presentation of two tones) – high/low Duration controlled: NA	70 dBSPL	Verbal	FR&DA	Right-handed reading-disabled group did not demonstrate a consistent REA More tonal stimuli recalled than CV, all groups More LE scores than RE
41.	Obrzut, J. E., Mondor, T. A., & Uecker, A. (1993)	CG: 34(15B &19G) MA: 9.2 ± 1.4 LD group: 17 MA:10.3 ± 1.1	DCV syllables (ba, da, pa, ta) Duration; 350 msec Duration controlled: NA	65 dBHL	Verbal	DA	Poor performance for DA(L)
42.	Morton, L. L., & Siegel, L. S. (1991)	CG: 30 LD group: 30 (28B & 2G) MA: 12.20 ± 1.39	DDT Duration, 306 msec (64 dichotic pairs of monosyllabic digits), 8 quadruple pairs	70 dBHL	Writing	FR&DA	No differences in laterality and overall recall performance LD & CG in the afternoon. Morning testing, CG showed greater REA for DA(R) and LEA for DA(L)
43.	Morton, L. L., & Kershner, J. R. (1993)	CG: 30 MA: 11.72 ± 0.74 LD group: 26(B) MA:11.24 ± 0.99	DDT 307 msec duration Eight quadruple Pairs	70 dB HL	Writing	FR&DA	Enhanced left hemisphere involvement after left hemisphere priming in the morning, and after right hemisphere priming in the afternoon
44.	Morton, L. L., & Siegel, L. S. (1991)	CG: 40 MA; 10.8 ± 1.1 LD group: 20 (comprehension) MA: 10.6 ± 0.9 LD group: 20 (comprehension and word recognition) MA:10.8 ± 0.7	DDT 307 msec duration 32 dichotic pairs (quadruple pairs) Duration controlled: NA	Intensity: NA	verbal	FR&DA	Reading disabled groups showed lower left ear advantage
45.	Boliek, C. A., Obrzut, J. E., & Shaw, D. (1988)	Control group: 25 (17B & 8G) MA:9.10 ± 1.7 LD group: 25 (17B & 8G) MA:10.1 ± 2.05	DCV Familiar CVC syllables & unfamiliar CV syllables	70-dB SPL	Verbal	FR&DA	Learning-disabled children did not demonstrate a consistent REA across all experimental conditions
46.	Yeni-Komshian, G. H., Isenberg, D., & Goldberg, H. (1975)	CG: 19 (9B & 10G) MA: 11.8 yrs LD group:19 (11B & 8G) MA: 12.8 yrs	DDT (8 digits except 6 and 7) 1/sec rate Duration controlled: yes	Normal conversational level	Verbal	DA	Overall, REA for both groups difference between the R and LE score was larger for LD group than CG
47.	Smith, K., & Griffiths, P. (1987)	CG: 12 (10B & 2G) MA: 11.36 yrs Dys group: 12 (10B & 2G) MA: 11.56 yrs	14 test pairs of non-phonological sounds.	65–75 dB	Verbal	FR&DA	-Significant LEA -Dyslexic children are unable to counteract the natural orienting tendency of their intact hemisphere
48.	Hugdahl, K., Helland, T., Færevaag, M. K., Lyssand, E. R. T., & Asbj rnsen, A. (1995)	CG: 53 Dys group: 53	DCV syllables 36 dichotic pairs	75 dB SPL	Pointing (selecting from a group)	FR	-Right-handed dyslexic subjects did not show the expected right ear advantage – left-handed group, there were no significant ear differences

CG – Control group, LD – learning disability group, RD – reading disability group, Dys – Individuals with dyslexia, B – Boys, G – Girls, MA – mean age, DCV – Dichotic CV, DDT – Dichotic digit test, FR – Free recall, DA – directed attention, REA – Right ear advantage, LEA – Left eat advantage, P – dyslexics; perceptual dyslexics, L – dyslexics; linguistic dyslexia, FRND – familial risk group of children who do not develop dyslexia, FRD – familial risk group of children who develop dyslexia, DD – Developmental dyslexia, RI/NLI – Reading impairment without impaired language comprehension, RI/LI – Reading impairment with impaired language comprehension, NA – not available.

Table 2. Mean values and CIs for Controls and LD.

Condition	Group	Stimulus	Right scores			Left Scores
			Pooled Mean	CI+	CI−	Pooled Mean	CI+	CI−
Free recall	Control	CV	31.34	33.54	29.15	22.38	24.31	20.45
		Digit	19.74	20.45	19.02	17.59	18.37	16.80
	LD	CV	26.22	28.61	23.84	21.45	23.47	19.43
		Digit	19.21	20.55	17.87	18.06	19.32	16.80
Directed right	Control	CV	30.60	34.57	26.63	–	–	–
		Digit	53.33	58.73	47.93	–	–	–
	LD	CV	28.75	32.59	24.90	–	–	–
		Digit	54.84	61.32	48.35	–	–	–
Directed left	Control	CV	–	–	–	22.33	25.31	19.35
		Digit	–	–	–	39.56	47.37	31.74
	LD	CV	–	–	–	25.51	28.40	22.62
		Digit	–	–	–	43	52.01	33.98

CI – confidence interval.

Figure 2. Forest plot indicating the performance difference between controls and LDs in dichotic CV test.

Figure 3. Forest plot indicating the performance difference between controls and LDs in dichotic digit test.

Figure 4. Forest plot indicating the right ear performance difference between controls and LDs in dichotic CV test.

Figure 5. Forest plot indicating the right ear performance difference between controls and LDs in dichotic digit test.

Figure 6. Forest plot indicating the left ear performance difference between controls and LDs in dichotic CV test.

Figure 7. Forest plot indicating the left ear performance difference between controls and LDs in dichotic digit test.

Figure 8. Forest plot indicating the right directed attention performance difference between controls and LDs in dichotic CV test.

Figure 9. Forest plot indicating the right directed attention performance difference between controls and LDs in dichotic Digit test.

Figure 10. Forest plot indicating the left-directed attention performance difference between controls and LDs in dichotic CV test.

Figure 11. Forest plot indicating the left-directed attention performance difference between controls and LDs in dichotic digit test.

Data availability statement

The data is available with the corresponding author and will be shared on request.