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Do you see what I see? The difference between dog and human visual perception may affect the outcome of experiments

Abstract and Figures

The visual sense of dogs is in many aspects different than that of humans. Unfortunately, authors do not explicitly take into consideration dog-human differences in visual perception when designing their experiments. With an image manipulation program we altered stationary images, according to the present knowledge about dog-vision. Besides the effect of dogs’ dichromatic vision, the software shows the effect of the lower visual acuity and brightness discrimination, too. Fifty adult humans were tested with pictures showing a female experimenter pointing, gazing or glancing to the left or right side. Half of the pictures were shown after they were altered to a setting that approximated dog vision. Participants had difficulty to find out the direction of glancing when the pictures were in dog-vision mode. Glances in dog-vision setting were followed less correctly and with a slower response time than other cues. Our results are the first that show the visual performance of humans under circumstances that model how dogs’ weaker vision would affect their responses in an ethological experiment. We urge researchers to take into consideration the differences between perceptual abilities of dogs and humans, by developing visual stimuli that fit more appropriately to dogs’ visual capabilities.
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:Szent István University, Research Institute for Animal Breeding and Nutrition, Hungary
;MTA-ELTE Comparative Ethology Research Group, Budapest, Hungary
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P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
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LAGF >GJ @ME9FK AK  $JA=:=D 9F< 0;@EA<  O@=J=9K L@= 4=:=J
>J9;LAGF >GJ <G?K AK  -J=LL=J=J =L 9D  9K=< GF L@=K= KLM<A=K
O= ;9F KL9L= L@9L L@= :JA?@LF=KK <AK;JAEAF9LAGF G> <G?K AK 9:GML LOG
LAE=K OGJK= L@9F L@9L G> @ME9FK
1@= L@AJ< <A>>=J=F;= AF NAKM9D H=J;=HLAGF :=LO==F <G?K 9F< @ME9FK
AK 9;MALQ 3AKM9D 9;MALQ AK 9 E=9KMJ= G> L@= KH9LA9D J=KGDMLAGF G> L@= NAKM9D
KQKL=E &L AK G>L=F E=9KMJ=< AF ;Q;D=K H=J <=?J==  -! O@A;@ AK L@=
FME:=J G> ;Q;D=K G> 9 ?J9LAF? GF= <9JC 9F< GF= DA?@L :9F< KM:L=F<=<
9L L@= =Q= H=J <=?J== 1@= E9PAEME NAKM9D 9;MALQ AK =IM9D LG L@= @A?@=KL
-! N9DM= O@=J= L@= ?J9LAF? AK KLADD H=J;=AN=< 9K :=AF? ;GEHJAK=< G> K=H
9J9L= :9F<K 1@= E9PAEME NAKM9D 9;MALQ G> L@= @ME9F =Q= AK 9JGMF< 
-! /MKK  9F<  -!  9EH:=DD 9F< $J==F  1@= E=9
KMJ=E=FLK G> <G?K NAKM9D 9;MALQ N9JQ :=LO==F  -! *MJH@Q =L 9D
 9F<  -! ,<GE =L 9D  ;;GJ<AF? LG L@=K= E=9KMJ=
E=FLK <G?K NAKM9D 9;MALQ AK >GMJ LG =A?@L LAE=K OGJK= L@9F L@9L G> @M
E9FK
!=KHAL= KM;@ =NA<=F;= J=?9J<AF? L@= <A>>=J=F;=K :=LO==F @ME9F 9F<
<G? NAKAGF L@=J= 9J= GFDQ N=JQ >=O =P;=HLAGFK O@=J= L@= 9ML@GJK E9<=
KGE= 9LL=EHLK LG <=KA?F =PH=JAE=FLK 9;;GJ<AF? LG L@= KH=;AY;ALA=K G>
<G? NAKAGF /9F?= =L 9D  L=KL=< <G?K AF 9F =PH=JAE=FL O@=J= L@=
KM:B=;LK @9< LG D=9JF LG ;9L=?GJAR= HA;LMJ=K 9;;GJ<AF? LG L@=AJ ;GFL=FL
<G?KNK D9F<K;9H=K OAL@ L@= @=DH G> 9 LGM;@K;J==F <=NA;= %=J= L@=
9ML@GJK E=FLAGF L@9L L@=Q 9;CFGOD=<?=< L@= <A>>=J=F;= :=LO==F <G?K
9F< @ME9FK;GDGJ NAKGF @GO=N=J AL @9K :==F 9DJ=9<Q HJGN=F L@9L L@AK
CAF< G> L9KC <G=K FGL J=IMAJ= ;GDGJ NAKAGF =? AF HA?=GFK MKL 9F<
%M:=J  ,L@=JOAK= AL AK OGJJAKGE= LG 9F =PL=FL L@9L =L@GDG?AKLK
K==EAF?DQ <G FGL L9C= AL AF ;GFKA<=J9LAGF L@9L <G?K EA?@L K== <A>>=J=FLDQ
L@= =PH=JAE=FL9D KLAEMDA L@9F L@= @ME9FK <G 9K 9FQ MF9;;GMFL=< <A>
>=J=F;= :=LO==F L@= NAKM9D H=J;=HLAGF G> <G?K 9F< @ME9FK ;GMD< J=KMDL
AF <G?K H=J;=ANAF? L@= NAKM9D KLAEMDA AF 9 O9Q FGL 9FLA;AH9L=< :Q L@= J=
K=9J;@=JK 1@AK ;GFK=IM=FLDQ E9Q D=9< LG HMRRDAF? J=KMDLK GJ LG 9 EAKAF
L=JHJ=L9LAGF G> <G?K:=@9NAGJ AF L@= L=KLK #GJ =P9EHD= <=H=F<AF? GF
L@= KLM<Q AF IM=KLAGF <G?K O=J= >GMF< LG := EGJ= GJ D=KK KM;;=KK>MD AF
>GDDGOAF? @ME9F ?D9F;=K *;(AFD=Q 9F< 09E:JGGC  0GHJGFA =L 9D
 E=9FO@AD= L@=Q O=J= EM;@ EGJ= =>>=;LAN= AF >GDDGOAF? L@= EGJ=
=NA<=FL 9JE KA?F9DK =? )9C9LGK =L 9D  -GF?Já;R =L 9D 9
0GHJGFA =L 9D  FGL@=J OA<=DQ MK=< L=KLAF? H9J9<A?E AK :9K=<
GF <G?KAFALA9D ;@GA;= :=LO==F LOG 9EGMFLK G> KE9DD >GG< H=DD=LK 
NK  -J9LG-J=NA<= =L 9D  DL@GM?@ L@= <A>>=J=F;= AF L@AK IM9F
LALQ <AK;JAEAF9LAGF L9KC K==EK G:NAGMK 9F< <=;AKAN= >GJ 9FQGF= L@=J= AK
=NA<=F;= *9JK@9DD-=K;AFA =L 9D  49J< 9F< 0EMLK  L@9L 9
;GFKA<=J9:D= FME:=J G> <G?K ;@GK= L@= KE9DD=J 9EGMFL G> >GG< AFKL=9<
G> L@= D9J?=J GFKA<=JAF? L@= O=9C=J 9;MALQ G> <G? NAKAGF L@= 9E:A?M
GMK J=KMDLK AF :GL@ L@= ?D9F;= >GDDGOAF? 9F< L@= IM9FLALQ <AK;JAEAF9LAGF
L=KLK ;GMD< := =PHD9AF=< @QHGL@=LA;9DDQ GF L@= :9KAK G> AF9<=IM9L= NAKM9D
H=J>GJE9F;=
Q L9CAF? AFLG 9;;GMFL L@= 9:GN= DAKL=< <A>>=J=F;=K AF L@= NAKM9D H=J
;=HLAGF G> <G?K 9F< @ME9FK J=K=9J;@=JK L@=GJ=LA;9DDQ K@GMD< <=KA?F =P
H=JAE=FLK :Q K=D=;LAF? EGJ= 9HHJGHJA9L= NAKM9D KLAEMDA >GJ L@=AJ KM:B=;LK
%GO=N=J K==AF? L@= =>>=;LK G> L@=K= <A>>=J=F;=K <AJ=;LDQ GF L@= 9;LM9D
KLAEMDA GJ GF L@= =PH=JAE=FL9D =FNAJGFE=FL ;GMD< := =N=F EGJ= @=DH
>MD AF L@= <=KA?F H@9K= G> L@= =PH=JAE=FL %GO=N=J KAEMD9LAF? <G?NA
KAGF >GJ @ME9FK OGMD< := N=JQ <A>Y;MDL =N=F A> O= OGMD< @9N= 9 EM;@
EGJ= <=L9AD=< CFGOD=<?= 9:GML L@= KH=;AY; H9J9E=L=JK G> L@= NAKM9D
H=J;=HLAGF G> <G?K \ :=;9MK= L@AK OGMD< J=IMAJ=  9 N=JQ KGH@AKLA
;9L=< L=;@FGDG?Q G> NAKM9D AE9?= HJ=K=FL9LAGF 9F<  =N=F A> L@= L=;@
FGDG?Q OGMD< := ?AN=F O= ;GMD< FGL := KMJ= O@=L@=J ;9FAF= 9F< @ME9F
:J9AFK HJG;=KK KAEAD9JDQ L@= NAKM9D K=FK9LAGF
1G :=?AF OAL@ 9F AE9?= HJG;=KKAF? LGGD L@9L ;GMD< 9HHJGPAE9L=DQ NA
KM9DAR= L@= E9AF <A>>=J=F;=K AF L@= NAKM9D H=J;=HLAGF G> L@= LOG KH=;A=K
OGMD< HJGNA<= 9 ?GG< A<=9 >GJ L@= =PH=JAE=FL=J LG EG<=D O@=L@=J
L@=J= ;GMD< := HJG:D=EK OAL@ 9 NAKM9D L9KC O@=F <G?K OGMD< := L@=
KM:B=;LK 1@=J= 9J= <=NA;=K L@9L 9J= 9DJ=9<Q 9N9AD9:D= >GJ L@AK HMJ
HGK= 0GE= G> L@=K= 9J= HDM?AFK >GJ AE9?= HJG;=KKAF? HJG?J9EK =?
GDGJDAF<F=KK 0AEMD9LGJK :Q -=LJA;@  L@=J=>GJ= AF GJ<=J LG
MK= L@=E GF= F==<K LG AFKL9DD L@=K= HJG?J9EK YJKL ,L@=JK LGGDK 9J=
UNCORRECTED PROOF
P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
EGJ= AFL=J9;LAN= 9F< JMF GF KE9JLH@GF=K =? !G? NAKAGF:Q +$%0
%GO=N=J L@=K= LGGDK 9J= GFDQ >GJ K@GOAF? L@= <A>>=J=F;=K AF ;GDGJ H=J
;=HLAGF L@=Q <G FGL E9C= AL HGKKA:D= LG <=EGFKLJ9L= L@= =>>=;L G>
<=;J=9K=< NAKM9D 9;MALQ 9F< L@= <=;J=9K=< :JA?@LF=KK <AK;JAEAF9LAGF
O@A;@ 9J= AEHGJL9FL ;GFLJA:MLGJK LG L@= <A>>=J=F;=K AF NAKM9D H=J;=HLAGF
K== =? 0;@GDLQKK=C =L 9D 
&F L@AK KLM<Q O= L=KL=< 9 F=O >J==DQ 9N9AD9:D= O=: :9K=< AE9?=
HJG;=KKAF? LGGD @LLH<G?NAKAGF;GE ;GHQJA?@L  - L@9L GN=J;GE=K
KGE= G> L@= DAEAL9LAGFK G> L@= HJ=K=FLDQ 9N9AD9:D= KGDMLAGFK 1@AK LGGD =F
9:D=K L@= MK=JK LG G:K=JN= L@= =>>=;LK G> <A;@JGE9;Q <=;J=9K=< :JA?@L
F=KK <AK;JAEAF9LAGF 9F< <=;J=9K=< NAKM9D 9;MALQ K=H9J9L=DQ GJ 9J:ALJ9JADQ
;GE:AF=< K== >MJL@=J <=L9ADK AF L@= HH=F<AP  &F GMJ =PH=JAE=FL O=
L=KL=< @ME9F KM:B=;LK OAL@ HA;LMJ=K AF L@=AJ GJA?AF9D 9F< 9DL=J=< >GJE
4= MK=< 9 EG<AY=< N=JKAGF G> L@= LOGG:B=;L ;@GA;= L=KL OAL@ @ME9F
HGAFLAF? K== 0GHJGFA =L 9D  O@=J= KM:B=;LK @9< LG <=;A<= O@A;@
KA<= O9K AF<A;9L=< :Q L@= <=HA;L=< @ME9F GF L@= AE9?= 1@J== LQH=K G>
<AJ=;LAGF9D AF<A;9LAGF O=J= HJ=K=FL=< AF :GL@ L@= @ME9F 9F< <G?NAKAGF
K=LLAF? HGAFL OAL@ =PL=F<=< 9JE @=9<LMJF 9F< ?D9F;= ,MJ E9AF IM=K
LAGF O9K O@=L@=J L@= 9;;MJ9;Q 9F< KH==< G> L@= KM:B=;LK9FKO=JK O=J=
9>>=;L=< :Q L@= NAKM9D K=LLAF? G> L@= HJ=K=FL9LAGFK O= @QHGL@=KAR=< L@9L
L@= EGJ= KM:LD= AK L@= <AJ=;LAGF9D AF>GJE9LAGF A= HGAFL OAL@ 9JE NK
?D9F;= L@= KLJGF?=J OADD := L@= <JGH AF L@= KM:B=;LKH=J>GJE9F;=
2. Materials and methods
2.1. Participants
#A>LQ 9<MDLK H9JLA;AH9L=< AF L@= KLM<Q 9K=< GF L@= DAL=J9LMJ= AF
LOGO9Q ;@GA;= =PH=JAE=FLK KAEAD9J LG L@= HJ=K=FL KLM<Q L@= 9N=J9?=
?JGMH KAR= >9DDK :=LO==F  9F<  AF<ANA<M9DK A= -GF?Já;R =L 9D
9 L@=J=>GJ= L@= N  ;9F := ;GFKA<=J=< 9K 9F =>>=;LAN= K9EHD=
KAR= %9D> G> L@= H9JLA;AH9FLK O=J= E=F 9N=J9?= 9?=  EAFAEME 
E9PAEME  Q=9JK L@= GL@=J @9D> O=J= OGE=F 9N=J9?= 9?=  EAF
AEME  E9PAEME  Q=9JK -9JLA;AH9LAGF O9K NGDMFL9JQ KM:B=;LK
O=J= J=;JMAL=< L@JGM?@ 9<N=JLAKAF? G> L@= L=KLK 9L L@= 2FAN=JKALQ ;9EHMK
KAL= 9F< L@JGM?@ H=JKGF9D 9;IM9AFL9F;=K 4= <A< FGL @9N= KH=;AY; J=
IMAJ=E=FLK >GJ L@= H9JLA;AH9FLK OAL@ L@= =P;=HLAGF L@9L A> L@=Q F==<=<
?D9KK=K;GFL9;L D=FK=K O= J=IM=KL=< L@=E LG O=9J L@=K= 9A<K <MJAF? L@=
L=KL 1@= HJGHGJLAGF G> H9JLA;AH9FLK O@G @9< ?D9KK=K;GFL9;L D=FK=K <A<
FGL <A>>=J :=LO==F L@= ?=F<=JK #AK@=J "P9;L L=KL /   -  
4JALL=F AF>GJE=< ;GFK=FL O9K G:L9AF=< >JGE 9DD KM:B=;LK 9 HJAGJA LG L@=
L=KL 1@= =PH=JAE=FL9D HJGLG;GD @9K :==F J=NA=O=< 9F< 9;;=HL=< :Q L@=
2FAL=< "L@A;9D /=NA=O GEEALL== >GJ /=K=9J;@ AF -KQ;@GDG?Q "-("
/=> +G 
2.2. Preparation of the test photographs
1=KL KM:B=;LK O=J= HJGNA<=< OAL@ H@GLG?J9H@K <=HA;LAF? 9 QGMF?
OGE9F O@G H=J>GJE=< L@= <AJ=;LAGF9D KA?F9DDAF? DD HA;LMJ=K K@GO=<
L@= K9E= H=JKGF 32 AF >JGFL G> 9 DA?@L :=A?= ;GDGJ=< L=PLAD= K@==L 
K=L G> =P=EHD9JK ;9F := K==F GF #A?  -@GLG?J9H@K O=J= L9C=F AF D9J?=
=FGM?@ IM9FLALQ L@9L O= ;GMD< MK= YN= <A>>=J=FL HA;LMJ=K G> =9;@ <AJ=;
LAGF9D KA?F9DDAF? LQH= LG :GL@ KA<=K D=>L 9F< JA?@L +G <A?AL9D EAJJGJAF?
GJ GL@=J =<ALAF? O9K H=J>GJE=< GF L@= HA;LMJ=K OAL@ L@= =P;=HLAGF G>
;GHQAF? L@= >MDD K=L G> ;@GK=F =PH=JAE=FL9D HA;LMJ= E9L=JA9D LG <G?NA
KAGF K=LLAF?
&L AK AEHGJL9FL LG =EH@9KAR= L@9L <M= LG L@= <A>>=J=F;=K AF L@= K=F
KALANALQ G> L@= @ME9F =Q= 9F< L@= AE9?AF? K=FKGJK 9F< <M= LG L@= DAE
AL9LAGFK AF L@= ;GDGJ J=HJG<M;LAGF ;9H9:ADALA=K G> L@= ;GEHML=J K;J==FK
FG AE9?= HJG;=KKAF? LGGD ;GMD< K@GO =P9;LDQ O@9L <G?K ;9F GJ ;9FFGL
H=J;=AN= %GO=N=J O= ;9F 9KKME= L@9L AE9?AF? 9F< AE9?= J=HJG<M;
AF? <=NA;=K @9N= :==F LMF=< LG E9L;@ L@= K=FKALANALQ G> L@= @ME9F =Q=
1@AK KAEHDAY;9LAGF =F9:D=K MK LG KAEMD9L= L@= <A>>=J=F;=K G> ;GDGJ H=J
;=HLAGF :=LO==F <G?K 9F< @ME9FK OAL@ L@= @=DH G> <A?AL9D AE9?=K GFDQ
Fig. 1. 1@J== H9AJK G> HA;LMJ=K >JGE L@= GJA?AF9D HJ=K=FL9LAGF -@GLG?J9H@K AF L@= YJKL ;GDMEF 9J= AF @ME9FNAKAGF K=LLAF? O@AD= L@= H@GLG?J9H@K AF L@= K=;GF< ;GDMEF O=J= 9DL=J=< LG
<G?NAKAGF K=LLAF? :Q L@= AE9?= HJG;=KKAF? LGGD @LLH<G?NAKAGF;GE "9;@ H9AJ G> H@GLG?J9H@K K@GOK GF= H9JLA;MD9J LQH= G> <AJ=;LAGF9D KA?F9D K== <=K;JAHLAGF GF L@= JA?@L
UNCORRECTED PROOF
P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
:Q L9CAF? AFLG 9;;GMFL L@= <A>>=J=F;=K :=LO==F L@= K=FKALANALQ G> L@= @M
E9F 9F< L@= ;9FAF= H@GLGJ=;=HLGJ KQKL=E 1@= =P9;L E=L@G< @GO L@=
AE9?= HJG;=KKAF? LGGD @LLH<G?NAKAGF;GE ;GHQJA?@L  - OGJCK
;9F := >GMF< AF L@= HH=F<AP 
2.3. Experimental process
1=KLK O=J= ;GF<M;L=< 9L L@= !=H9JLE=FL G> "L@GDG?Q O@=J= L@= KM:
B=;LK O=J= L=KL=< GF= :Q GF= OAL@ L@= 9KKAKL9F;= G> L@= =PH=JAE=FL=J
32 AF 9 IMA=L K=EA<9JC JGGE -9JLA;AH9FLK O=J= AFKLJM;L=< 9:GML
L@= :9KA; ;AJ;MEKL9F;=K G> L@= =PH=JAE=FL OAL@GML =PHDA;AL 9HJAGJA AF
>GJE9LAGF 9:GML L@= LQH=K G> <AJ=;LAGF9D KA?F9DK L@=Q OADD K== GF L@=
HA;LMJ=K 1=KL HA;LMJ=K O=J= HJ=K=FL=< :Q 9F< L@= H9JLA;AH9FLK9FKO=JK
O=J= J=;GJ<=< OAL@ L@= ,H=F0=K9E=  KG>LO9J= 1=KL HA;LMJ=K O=J=
K@GOF GF 9 >MDD%! ;GEHML=J K;J==F G>  × HAP=DK J=KGDMLAGF
-9JLA;AH9FLK O9L;@=< L@= HJ=K=FL9LAGFK  E 9O9Q >JGE L@= K;J==F 1@=
=PH=JAE=FL=JK H@GLG?J9H@ O9K  E L9DD GF L@= K;J==F J=KMDLAF? AF
9  E 9HH9J=FL KAR= >JGE L@= NA=O=JK <AKL9F;= 1@AK E=9FK L@9L GMJ
HJ=K=FL9LAGF J=K=E:D=< LG 9 J=9D K;=F9JAG O@=J= L@= =PH=JAE=FL=J KA?
F9DK 9HHJGPAE9L=DQ  E 9O9Q >JGE L@= KM:B=;L 9 <AKL9F;= L@9L AK JGM
LAF=DQ MK=< AF HGAFLAF? =PH=JAE=FLK =? %=?=<üK =L 9D  -GF?Já;R
=L 9D : 0GHJGFA =L 9D 
"9;@ KM:B=;L NA=O=< 9F AF<ANA<M9DDQ 9KK=E:D=< KDA<= K@GO ;GFKAKL
AF? G>  H@GLG?J9H@K "9;@ H@GLG?J9H@ K@GO=< L@= =PH=JAE=FL=J HJ=
K=FLAF? GF= G> L@J== HGKKA:D= <AJ=;LAGF9D KA?F9DK HGAFL OAL@ =PL=F<=<
9JE " DGGC LG GF= KA<= :Q LMJFAF? @=J @=9< %1 ?D9F;= LG GF= KA<=
O@AD= >9;AF? 9@=9< $) 9F< 9DKG 9 >GMJL@ LQH= <M::=< 9K FG <AJ=;
LAGF9D AF>GJE9LAGFGJ DGGC 9@=9< ) 1@= J9F<GEDQ AFK=JL=< ) HA;
LMJ=K O=J= MK=< 9K 9 :M[=J 9?9AFKL HGKKA:D= >9KL D=9JFAF? G> <AJ=;LAGF9D
;M=K :Q L@= H9JLA;AH9FLK #JGE =9;@ KA?F9D LQH= =IM9D 9EGMFL G> D=>L
9F< JA?@L N=JKAGFK O=J= HJ=K=FL=< OAL@ 9 <GM:D= 9EGMFL G> ) HA;
LMJ=K <<ALAGF9DDQ @9D> G> L@= HA;LMJ=K O=J= HJ=K=FL=< AF @ME9FNA
KAGF 9F< L@= GL@=J @9D> AF <G?NAKAGF K=LLAF? 4= MK=< YN= N=JKAGFK G>
=9;@ HA;LMJ= LQH= 9F< L@= K9E= =P9;L HA;LMJ= O9K MK=< GFDQ GF;= OAL@AF
L@= NAKAGFK=LLAF?K 1@=J=>GJ= L@= YF9D HA;LMJ= ;GMFL O9K  <AJ=;LAGF9D
KA?F9D LQH= × KA<= × NAKAGF K=LLAF? LQH= ×   -A;LMJ=K O=J=
HJ=K=FL=< AF 9 K=EAJ9F<GE GJ<=J OAL@ LOG J=KLJA;LAGFK L@= YJKL LOG
HJ=K=FL9LAGFK O=J= 9DO9QK AF @ME9FNAKAGF K=LLAF? 9F< HA;LMJAF? <AJ=;
LAGF9D KA?F9DK GL@=J L@9F ) 9F< L@= K9E= KA<= O9K AF<A;9L=< E9PAEME
LOA;= AF 9 JGO
L L@= :=?AFFAF? =9;@ KM:B=;L K9O L@= K9E= AFKLJM;LAGF GF L@=
K;J==F
,F O@A;@ KA<= AK L@= :9DD
5GM ;9F 9FKO=J :Q HJ=KKAF? L@= D=>LGJ JA?@L9JJGO C=Q
!=;A<= IMA;CDQ QGM @9N= GFDQ  K LG ;@GGK=
-ML QGMJ YF?=JK GF L@= 9JJGO C=QK HD=9K= 9F< HJ=KK 9FQ G> L@=E
LG KL9JL
!MJAF? L@= L=KL 9 F=O HA;LMJ= =E=J?=< =N=JQ LAE= L@= KM:B=;L HJ=KK=<
GF= G> L@= 9JJGO C=QK GJ 9>L=J  K O9K =D9HK=< 1@= KG>LO9J= ?=F=J9L=<
9 ;KN YD= >JGE L@= 9FKO=JK J=;GJ<AF? L@= ;GJJ=;LF=KK G> ;@GA;= 9F< L@=
J=KHGFK= LAE= &F ;9K= G> D9;C G> 9FKO=J OAL@AF  K 9F 9MLGE9LA; AF;GJ
J=;L 9FKO=J O9K J=;GJ<=< ,:NAGMKDQ AF ;9K= G> L@= ) HA;LMJ=K F=AL@=J
D=>L GJ JA?@L O9K 9 ;GJJ=;L J=KHGFK= AF L@AK ;9K= L@= HJG?J9E HJ=<=
YF=< 9F 9J:ALJ9JQ ;GJJ=;LAF;GJJ=;L <AKLJA:MLAGF G> 9FKO=JK
2.4. Statistical analyses
4= H=J>GJE=< $=F=J9DAR=< )AF=9J *AP=< *G<=DK 9F9DQKAK GF L@=
FME:=J G> ;GJJ=;L 9FKO=JK 4= MK=< L@= ?=F<=J G> L@= H9JLA;AH9FLK
E9D= NK >=E9D= L@= LQH= G> L@= <AJ=;LAGF9D KA?F9D " %1 GJ $) 9F<
L@= LQH= G> L@= HJ=K=FL9LAGF @ME9F GJ <G?NAKAGF 9K #AP=< =>>=;LK 9F<
L@= &! G> L@= AF<ANA<M9DK 9K /9F<GE >9;LGJ 1@= J=KHGFK=K LG ) HA;LMJ=K
O=J= FGL AF;DM<=< AF L@= 9F9DQKAK =KA<=K L@= E9AF =>>=;LK O= 9F9DQR=<
L@= O9Q AFL=J9;LAGFK G> L@= 9:GN= E=FLAGF=< L@J== YP=< =>>=;LK 1@=
FGJE9DALQ G> GMJ <9L9 O9K 9F9DQR=< :Q L@= NAKM9D =P9EAF9LAGF G> L@= ..
HDGLK G> J=KA<M9DK 1G G:L9AF L@= KAEHD=KL EG<=D L@9L KM>Y;A=FLDQ =PHD9AFK
GMJ <9L9 O= 9HHDA=< :9;CO9J< =DAEAF9LAGF EG<=D K=D=;LAGF =P;DM<AF?
AFL=J9;LAGFK OAL@ L@= @A?@=KL HN9DM= KL=H:QKL=H LADD O= J=9;@=< =>>=;LK
OAL@ DGO=J L@9F  H N9DM=K &F L@= >GDDGOAF? O= J=HGJL L@= G:L9AF=<
YF9D EG<=DK GFDQ -GKL@G; L=KLK O=J= H=J>GJE=< 9K H9AJOAK= ;GEH9J
AKGFK G> L@= D=N=DK G> L@= KA?FA>A;9FL =>>=;LK 9F< ;GFLJGDD=< >GJ EMDLAHD=
;GEH9JAKGFK OAL@ 0=IM=FLA9D 0A<9C E=L@G< 1@=K= ;GJJ=;L=< HN9DM=K
9J= J=HGJL=< AF 9DD HGKL@G; J=KMDLK 1@=K= KL9LAKLA;9D 9F9DQK=K O=J= H=J
>GJE=< :Q L@= &* 0-00 0L9LAKLA;K  KG>LO9J=
1G 9F9DQR= L@= /=KHGFK= LAE=K 9K L@=K= ;9F := ;=FKGJ=< >JGE :GL@
KA<=K O= 9HHDA=< GP *AP=<=>>=;LK J=?J=KKAGF EG<=D / / GJ= 1=9E
 ;GPE= H9;C9?= 1@=JF=9M  OAL@ L@= KM:B=;L A<=FLALQ 9K
J9F<GE >9;LGJ 1G YF< L@= :=KL EG<=D O= MK=< >GJO9J< 9HHJG9;@ 9F<
AF;DM<=< L@= E9AF =>>=;LK 9F< AFL=J9;LAGFK KL=H:QKL=H LG AF;J=9K= L@=
;GEHD=PALQ 9F< L=KL=< L@= DG?DAC=DA@GG< ;@9F?= :=LO==F EG<=DK &> L@=
AF;DMKAGF G> 9F =>>=;L <A<FL J=KMDL AF KA?FA>A;9FL ;@9F?= O= J=EGN=< AL
>JGE L@= EG<=D 4= L=KL=< L@= K9E= =>>=;LK 9K AF L@= ;9K= G> L@= ;GJJ=;L
;@GA;=K K== 9:GN= 0M:B=;L ?=F<=J @9< FG KA?FA>A;9FL =>>=;L L@MK O=
D=>L AL GML >JGE L@= YF9D EG<=D O@A;@ AF L@AK O9Q ;GFL9AF=< L@= LQH=
G> <AJ=;LAGF9D KA?F9D 9F< LQH= G> HJ=K=FL9LAGF 9K E9AF =>>=;LK 9F< L@=AJ
AFL=J9;LAGF
3. Results
&F L@= ;9K= G> L@= FME:=J G> ;GJJ=;L 9FKO=JK L@= EG<=D K@GO=< 9
KA?FA>A;9FL =>>=;L #    H   K 9DD L@= YP=< >9;LGJK
9HH=9J=< AF L@= KA?FA>A;9FL O9Q AFL=J9;LAGFK O= <A< FGL 9F9DQR= L@=
E9AF =>>=;LK K=H9J9L=DQ 1@=J= O9K 9 KA?FA>A;9FL AFL=J9;LAGF :=LO==F L@=
LQH= G> HJ=K=FL9LAGF 9F< LQH= G> <AJ=;LAGF9D KA?F9D #   
H   O@=J= 9;;GJ<AF? LG L@= HGKL @G; L=KL H9JLA;AH9FLK K@GO=<
9 O=9C=J H=J>GJE9F;= AF ;9K= G> $) O@=F AL O9K HJ=K=FL=< AF <G?NA
KAGF K=LLAF? #MJL@=JEGJ= O@=F L@= <AJ=;LAGF9D KA?F9DK O=J= HJ=K=FL=<
AF L@= <G?NAKAGF K=LLAF? H9JLA;AH9FLK K@GO=< KA?FA>A;9FLDQ :=LL=J H=J
>GJE9F;= AF ;9K= G> " 9F< %1 L@9F HA;LMJ=K K@GOAF? $) #A?  4=
>GMF< 9DKG 9 KA?FA>A;9FL AFL=J9;LAGF :=LO==F L@= ?=F<=J G> H9JLA;AH9FLK
9F< L@= LQH= G> HJ=K=FL9LAGF #    H   ;;GJ<AF?
LG L@= HGKL @G; 9F9DQKAK E=F H=J>GJE=< HGGJ=J AF L@= ;9K= G> HJ=K=FL9
LAGFK AF L@= <G?NAKAGF K=LLAF? #A?  $=F<=J G> H9JLA;AH9FLK @9< 9 KA?
Fig. 2. +ME:=J G> ;GJJ=;L 9FKO=JK AF ;9K= G> L@J== LQH=K G> <AJ=;LAGF9D KA?F9DK HJ=K=FL=<
AF @ME9F 9F< <G? NAKAGF K=LLAF? N  H9JLA;AH9FLK 9JK J=HJ=K=FL L@= FME:=J G> ;GJ
J=;L 9FKO=JK AF L@= ;9K= G> <A>>=J=FL <AJ=;LAGF9D KA?F9DK 9F< LQH= G> HJ=K=FL9LAGF !A>>=J=FL
D=LL=JK AFKA<= L@= :9JK K@GO KA?FA>A;9FL <A>>=J=F;=K OAL@AF 9 HJ=K=FL9LAGF LQH= ;9HAL9DK @M
E9F NAKAGF DGO=J ;9K= <G? NAKAGF $=F=J9DAR=< )AF=9J *AP=< *G<=DD 9KL=JAKC AF<A;9L=K
KA?FA>A;9FL <A>>=J=F;= OAL@AF 9 <AJ=;LAGF9D KA?F9D LQH=  -  
UNCORRECTED PROOF
P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
Fig. 3. +ME:=J G> ;GJJ=;L 9FKO=JK ?AN=F :Q E9D= N  9F< >=E9D= N  KM:B=;LK
9JK J=HJ=K=FL L@= FME:=J G> ;GJJ=;L 9FKO=JK AF L@= ;9K= G> E9D= 9F< >=E9D= H9JLA;AH9FLK
AF <A>>=J=FL LQH=K G> NAKM9D HJ=K=FL9LAGF $=F=J9DAR=< )AF=9J *AP=< *G<=DD 9KL=JAKC AF<A
;9L=K KA?FA>A;9FL <A>>=J=F;= :=LO==F L@= HJ=K=FL9LAGF LQH=K  -  
FA>A;9FL AFL=J9;LAGF OAL@ L@= LQH= G> <AJ=;LAGF9D KA?F9DK 9K O=DD #
   H   ;;GJ<AF? LG L@= HGKL @G; 9F9DQKAK E=F
K@GO=< :=LL=J H=J>GJE9F;= AF L@= ;9K= G> %1 L@9F $) 4GE=F H=J
>GJE=< :=KL AF L@= ;9K= G> " 9F< L@=Q K@GO=< L@= O=9C=KL H=J>GJ
E9F;= 9DKG AF L@= ;9K= G> $) 1@= KM;;=KK G> OGE=F AF L@= ;9K= G> %1
O9K :=LO==F " 9F< $)
1@= GP EG<=D HJGN=< LG := KA?FA>A;9FL AF L@= ;9K= G> J=KHGFK=
LAE= AF;DM<AF? 9F AFL=J9;LAGF :=LO==F L@= LQH= G> HJ=K=FL9LAGF 9F<
L@= LQH= G> <AJ=;LAGF9D KA?F9D χ   H   KM??=KL
AF? 9 KLJGF? =>>=;L G> <G? NAKAGF AF L@= ;9K= G> $) HJ=K=FL9LAGF LQH=
GFDQ 1@= J=KMDL K@GO L@9L ;GEH9J=< LG @ME9F NAKAGF L@=J= O9K FG
KA?FA>A;9FL <A>>=J=F;= AF <G? NAKAGF :=LO==F L@= HGAFLAF? 9F< DGGCAF?
=PHβ   K=   6  \ H   O@AD= L@= HJ=K=F
L9LAGF G> ?9RAF? AF <G? NAKAGF DGO=J=< L@= ;@9F;= G> IMA;C=J J=KHGFK= :Q
 =PHβ   K=   6  \ H   #A? 
4. Discussion
&F GMJ =PH=JAE=FL @ME9F H9JLA;AH9FLK @9< LG <=;A<= O@=L@=J 9
QGMF? OGE9F AF<A;9L=K L@= D=>L GJ JA?@L <AJ=;LAGF OAL@ =AL@=J @=J =P
L=F<=< 9JE @=9< LMJFAF? GJ ?D9F;= %9D> G> L@= HJ=K=FL9LAGFK 9HH=9J=<
9K 9 @ME9F OGMD< K== L@=E @GO=N=J L@= GL@=J @9D> O=J= 9DL=J=< LG 9
F=O K=LLAF? O@=J= L@= @QHGL@=KAR=< ;GDGJJ9F?= :JA?@LF=KK 9F< J=KG
DMLAGF 9JJ9F?=E=FLK O=J= ;J=9L=< 9;;GJ<AF? LG L@= N9DM=K <J9OF >JGE
L@= =PAKLAF? DAL=J9LMJ= 9:GML <G?NAKAGF 1@= J=KMDLK K@GO=< L@9L KM:B=;LK
;GMD< >GDDGO 9FQ G> L@= <AJ=;LAGF9D KA?F9DK AF @ME9F H=J;=HLAGF EG<=
9F< AF L@= ;9K= G> HGAFLK OAL@ 9JE 9F< @=9< LMJFK AF <G?NAKAGF K=LLAF?
%GO=N=J AF ;9K= G> ?D9F;AF? H9JLA;AH9FLK H=J>GJE=< KA?FA>A;9FLDQ OGJK=
O@=F L@= HJ=K=FL9LAGF EAEA;C=< <G?KNAKM9D H=J;=HLAGF 9F< ?D9F;=K
O=J= L@= @9J<=KL LG >GDDGO >JGE 9EGF? L@= <AJ=;LAGF9D KA?F9DK HJ=K=FL=<
AF <G?NAKAGF K=LLAF? &FL=J=KLAF?DQ H9JLA;AH9FLK?=F<=J 9DKG 9>>=;L=< L@=
H=J>GJE9F;= E=F AF ?=F=J9D H=J>GJE=< HGGJ=J AF <G?NAKAGF L@9F AF
@ME9F NAKAGF K=LLAF? 1@AK YF<AF? AK H9J9DD=D OAL@ =9JDA=J J=KMDLK O@=J=
E=FK H=J>GJE9F;= O9K O=9C=J AF L9KCK O@=J= J=Z=PAN= K@A>LK G> 9LL=F
LAGF LG ?9R=<9L <AJ=;LAGFK @9N= :==F L=KL=< >GJ 9F< AF ?=F=J9D O@=F
L@= LOG ?=F<=JKH=J>GJE9F;= O9K ;GEH9J=< AF >GDDGOAF? KQE:GDA; <A
J=;LAGF9D ;M=K 9QDAKK =L 9D  /=KHGFK= LAE= AF GMJ KLM<Q 9DKG AF
<A;9L=< @GO <A>Y;MDL AL O9K LG <=;AH@=J ?D9F;AF? O@=F HA;LMJ=K O=J=
9DL=J=< LG 9F 9HHJGPAE9L= <G?NAKAGF -9JLA;AH9FLK J=KHGF<=< KDGO=J LG
?D9F;=K L@9F LG L@= GL@=J LOG <AJ=;LAGF9D KA?F9DK
&F L@AK H9H=J O= AFLJG<M;=< 9 F=O AE9?= E9FAHMD9LAGF LGGD L@9L 9L
L=EHLK LG <AKHD9Q AE9?=K 9>L=J 9 ;GEHD=P 9DL=J9LAGF HJG;=<MJ= HJGNA<
AF? 9F 9HHJGPAE9LAGF G> <G?KNAKM9D K=FK9LAGFK ,MJ @QHGL@=KAK O9K
L@9L L@= ?=F=J9DDQ O=9C=J NAKM9D H=J;=HLAGF G> <G?K OGMD< J=KMDL AF
DGO=J H=J>GJE9F;= AF KM;@ L9KCK O@=J= L@= AEHGJL9FL <=L9ADK 9J= J=D9
LAN=DQ YF= 1@= H=J>GJE9F;= G> L@= @ME9F H9JLA;AH9FLK HJGN=< L@9L A>
L@= GL@=JOAK= O=DD NAKA:D= ?D9F;=K O=J= <=L=JAGJ9L=< OAL@ L@= AE9?= E9
FAHMD9LAF? HJG?J9E LGO9J<K L@= NAKM9D H9J9E=L=JK L@9L 9J= ;DGK=J LG L@=
D=N=D 9K 9 <G? OGMD< HJG:9:DQ H=J;=AN= L@=E @ME9FK >GDDGO=< L@=E
OAL@ D=KK KM;;=KK 9F< KDGO=J L@9F GL@=J EGJ= JG:MKL NAKM9D ;M=K D
L@GM?@ L@= ;GDD=;L=< <9L9 9J= AF<AJ=;L :=;9MK= L@=Q 9J= :9K=< GF @M
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Fig. 4. 1@= ;MEMD9LAN= HJGHGJLAGF G> J=KHGFK=K ;GEH9J=< :=LO==F HJ=K=FL9LAGF 9F< <AJ=;LAGF9D KA?F9D LQH=K N  H9JLA;AH9FLK 1@= <A>>=J=FL DAF=K J=HJ=K=FL L@= LQH= G> <AJ=;LAGF9D
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UNCORRECTED PROOF
P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
J9F<GEDQ &F L@= ;9K= G> =PH=JAE=FLK O@=J= <G?K @9N= LG <=;A<= MHGF
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J=KHGFK=K DL@GM?@ <G?K HJGN=< LG := K=FKALAN= LG L@= 9LL=FLAN= >G;MK G>
9 @ME9F 3AJáFQA =L 9D  AL AK MFCFGOF O@=L@=J L@= EGLAGF ;GE
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?=L@=J 1=;@FAIM=K L@9L AFL=F< LG L=KL NAKM9D ;9H9;ALQ G> FGF@ME9F 9FA
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GFDQ L@= ;GDGJ G> L@= HJ=K=FL9LAGFK E9Q D=9< LG H9J9<GP J=KMDLK ;D9AE
AF? L@9L 9FAE9DK OAL@ GFDQ GF= LQH= G> ;GF= ;=DD AF L@=AJ J=LAF9 E9Q :=
9:D= LG <AKLAF?MAK@ 9EGF? ;GDGJK =? $JA=:=D 9F< 0;@EA<  
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O9K MF<=J ;GFLJGD AL LMJF=< GML L@9L 9L D=9KL @9J:GJ K=9DK 9J= ;GE
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E=L@G< MK=< >GJ GMJ KLM<Q @=J= ;J=9L=K KM;@ NAKM9D HJ=K=FL9LAGFK L@9L
<AN=J?= >JGE L@= GF=K @ME9FK MK=< LG K== AF L@J== AEHGJL9FL H9J9E=
L=JK OAL@ L@= =P;=HLAGF G> L@= <QF9EA; ;GEHGF=FLK L@9L <A>>=J=FLA9L=K
;9FAF= 9F< @ME9F NAKAGF
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?AKLK =EHDGQ=< =JJGF=GMK GJ AFKM>Y;A=FL E=L@G<K O@=F L@=Q O=J= L=KL
AF? <G?K AF NAKM9D <AK;JAEAF9LAGF L9KCK AF L@= H9KL 1@= DGF? DAKL G>
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MKM9DDQ GF 9;;=HL9:D= D=N=DK >GJ <J9OAF? ;GF;DMKAGFK :9K=< GF L@= 9N=J
9?= H=J>GJE9F;= G> L@= ?JGMHK %GO=N=J O@9L AK MKM9DDQ FGL J=HGJL=< AF
L@= J=KMDLK :ML K;A=FLAKLK >9;= 9K 9F =N=JQ<9Q FMAK9F;= @A?@ <JGHGML
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L=KLK GJ 9 @A?@ KL9F<9J< <=NA9LAGF N9DM= AF KGE= G> L@= =PH=JAE=FL9D
?JGMHK L@=K= E9Q := L@= J=KMDLK G> HGGJ =PH=JAE=FL9D <=KA?F <M= LG L@=
NAKM9DDQ ;@9DD=F?AF? HJ=K=FL9LAGFK >GJ <G?K DL@GM?@ AF9<=IM9L= EG
LAN9LAGF D=N=D G> L@= KM:B=;LK HJG:D=EK OAL@ L@= KLJ=KK>MD L=KL =FNAJGF
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L@= N=J?= G> NAKM9D ;9H9;ALQ G> <G?K E9Q 9DKG := L@= C=Q LG KM:GHLAE9D
H=J>GJE9F;= &F L@= ;9K= G> L@= D9LL=J GL@=J >9;LGJK KM;@ 9K DA?@L ;GF<A
LAGFK <AKL9F;= >JGE L@= L9J?=L =L; E9Q 9DKG <=;A<= L@= 9;LM9D GML;GE=
G> 9F =PH=JAE=FL
4= 9J= ;GFNAF;=< L@9L L9CAF? AFLG 9;;GMFL L@= <A>>=J=F;=K AF H=J;=H
LAGF OADD D=9< LG =PH=JAE=FL9D <=KA?FK L@9L @9N= 9 @A?@=J J9L= G> KM;;=KK
9F< L@9L QA=D< MF9E:A?MGMK J=KMDLK 1@AK E=9FK EGJ= =>Y;A=FL ;GF<M;L
AF? G> KLM<A=K 9F< D=KK Z9O=< <=KA?FK L@9L OGMD< GL@=JOAK= O9KL= LAE=
:Q F=;=KKAL9LAF? 9 J=JMF G> L@= L=KLK ,MJ KLM<Q HJGNA<=< KGE= AFKA?@L LG
9 K;=F9JAG O@=J= @ME9FK @9< LG H=J>GJE AF 9 NAKM9D L9KC O@=J= AE9?=K
O=J= E9FAHMD9L=< AF 9 ;GEHD=P O9Q MKAF? ;GDGJ :JA?@LF=KK 9F< J=KG
DMLAGF N9DM=K :9K=< GF GMJ CFGOD=<?= 9:GML ;9FAF= NAKAGF 1@= O=9C=J
H=J>GJE9F;= G> GMJ KM:B=;LK AF ;9K= G> E9FAHMD9L=< AE9?=K K@GMD< MJ?=
=PH=JAE=FL=JK LG <G EGJ= :9KA; J=K=9J;@ GF L@= KH=;AY; J=IMAJ=E=FLK G>
HJGH=J NAKM9D HJ=K=FL9LAGFK >GJ ;9FAF= KM:B=;LK
Acknowledgements
1@AK KLM<Q O9K >MF<=< :Q L@= %MF?9JA9F ;9<=EQ G> 0;A=F;=K *1
  !MJAF? L@= LAE= G> E9FMK;JAHL HJ=H9J9LAGF 1# O9K 9DKG KMH
HGJL=< :Q L@= 0L9FLGF #GMF<9LAGF +=PL $=F=J9LAGF 9FAF= /=K=9J;@
$J9FL 1@= 9ML@GJK 9J= L@9FC>MD LG =D=KL= / -GF?Já;R >GJ L@= "F?DAK@
HJGG>J=9<AF? G> L@= E9FMK;JAHL
Appendix A.
Visualizing the di9erences in color perception
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D=N=D G> =P;AL9LAGF G> L@= L@J== H@GLG HA?E=FL LQH=K AF L@= @ME9F =Q=
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:Q L@= J=< H@GLG HA?E=FL 9J= 9DKG 9:KGJ:=< :Q L@= ?J==F H@GLG HA?E=FL
9D:=AL OAL@ 9 DGO=J AFL=FKALQ
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GF= :=AF? J=< 9F< L@= GL@=J ?J==F OGMD< := H=J;=AN=< :Q 9 <G? 9K
@9NAF? 9DEGKL L@= K9E= @M= :ML <A>>=JAF? AF :JA?@LF=KK L@= J=< GF=
H=J;=AN=< <9JC=J L@9F L@= ?J==F 1@= =P9;L :JA?@LF=KK <A>>=J=F;= H=J
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L@= J=Z=;L=< DA?@L 9F< L@= F=MJ9D HJG;=KKAF? AF L@= <G?K NAKM9D ;GJ
L=P 9K=< GF L@= GN=JD9H G> L@= K=FKALANALQ ;MJN= G> L@= @ME9F J=< 9F<
?J==F H@GLG HA?E=FLK O= =KLAE9L=< L@9L 9 J=< KMJ>9;= OGMD< := H=J
;=AN=< :Q 9 <G? 9K @9NAF? GFDQ  G> L@= :JA?@LF=KK G> 9 ?J==F KMJ
>9;= ;;GJ<AF? LG L@AK L@= ;GDGJ N9DM=K >GJ L@= KAEMD9L=< AE9?= 9J=
;9D;MD9L=< >JGE L@= GJA?AF9D N9DM=K 9K >GDDGOK SimBlue OrigBlueSim-
Green  7OrigGreen  OrigRed ×8 1G 9;@A=N= L@9L O@9L L@=
<G?K K== 9K 9 F=MLJ9D @M= OADD 9DKG := F=MLJ9D GF L@= KAEMD9L=< AE9?=
>GJ L@= @ME9F =Q= L@= J=< ;GDGJ N9DM= AF L@= KAEMD9L=< AE9?= AK E9<=
UNCORRECTED PROOF
P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
=IM9D LG L@= ?J==F ;GDGJ N9DM= SimRed SimGreen  <=EGFKLJ9LAGF
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:=>GJ= 9FQ GH=J9LAGF L@9L OGMD< J=IMAJ= DAF=9JALQ G> L@= <9L9 L@= DMEA
F9F;= N9DM=K @9N= LG := ?9EE9 =PH9F<=< 9F< 9>L=J L@= E9FAHMD9LAGF
?9EE9 ;GEHJ=KK=< 4= 9HHDA=< L@=K= KL=HK =9;@ LAE= :=>GJ= 9F< 9>L=J
E9FAHMD9LAF? L@= AE9?= <9L9
Visualizing the di9erences in brightness discrimination
1G NAKM9DAR= L@= LOG LAE=K O=9C=J :JA?@LF=KK <AK;JAEAF9LAGF G> <G?K
L@= :JA?@LF=KK J9F?= G> L@= AE9?= @9K LG := <=;J=9K=< :Q 9 >9;LGJ G>
LOG 1@AK ;9F := <GF= :Q <ANA<AF? L@= /$ ;GDGJ N9DM=K :Q LOG :ML L@AK
9DKG D=9<K LG 9 <9JC=FAF? G> L@= AE9?= 1G ;GEH=FK9L= >GJ L@AK =>>=;L
L@= 9N=J9?= :JA?@LF=KK G> L@= GJA?AF9D AE9?= @9K LG := ;9D;MD9L=< YJKL
4@=F ;9D;MD9LAF? L@= 9N=J9?= :JA?@LF=KK L@= L@J== ;GDGJ ;@9FF=DK 9J=
L9C=F AFLG 9;;GMFL OAL@ <A>>=J=FL O=A?@LK LG 9;;GMFL >GJ L@= <A>>=JAF?
K=FKALANALQ G> L@= @ME9F =Q= >GJ =9;@ @M= 78 AvgBrightness  AvgOri-
gRed ×  AvgOrigGreen ×  AvgOrigBlue × >L=J
G:L9AFAF? L@= 9N=J9?= :JA?@LF=KK L@= :JA?@LF=KK J9F?= G> L@= AE9?=
AK ;GEHJ=KK=< :Q 9HHDQAF? L@= >GDDGOAF? >GJEMD9 LG =N=JQ /$ ;GDGJ
N9DM= SimRGB  OrigRGB AvgBrightness 
Fig. A1.  ;GEHD=L= /$ ;GDGJ KH=;LJME 9:GN= 9F< L@= K9E= KH=;LJME HJG;=KK=< :Q
L@= 9D?GJAL@E L@9L HJG<M;=K L@= <=ML=J9FGHA9 =>>=;L :=DGO
Fig. A2.  ;GFLAFMGMK ?J9<A=FL >JGE :D9;C LG O@AL= 9:GN= 9F< L@= K9E= ?J9<A=FL
HJG;=KK=< :Q L@= 9D?GJAL@E L@9L @9DN=< L@= <QF9EA; J9F?= :=DGO
Fig. A3. D9;C 9F< O@AL= ?J9LAF?K OAL@ 9 :9J OA<L@ G>  HAP=DK 1@= LGHEGKL AE9?= AK
L@= GJA?AF9D :=DGO >JGE LGH LG :GLLGE AK L@= K9E= ?J9LAF? K@GOAF? L@= =>>=;LK G> <=;J=9K=<
NAKM9D 9;MALQ :Q 9 >9;LGJ G> LOG LG =A?@L
<=EGFKLJ9LAGF G> L@= =>>=;L G> L@= :JA?@LF=KK J9F?= <=;J=9K=< :Q 9 >9;LGJ
G> LOG ;9F := G:K=JN=< GF #A? 
Visualizing the di9erences in visual acuity
0@GOAF? L@= =>>=;LK G> <=;J=9K=< NAKM9D 9;MALQ ;9F := 9;@A=N=< :Q
:DMJJAF? L@= AE9?= ,F= E=L@G< LG 9;@A=N= L@AK AK LG 9N=J9?= L@= N9DM=K
G> F=A?@:GJAF? HAP=DK #GJ H=J>GJE9F;= J=9KGFK 9 DAF=9J :DMJ 9D?GJAL@E
O9K MK=< 1@AK 9D?GJAL@E HJG;=KK=K L@= AE9?= AF LOG H9KK=K 9 @GJARGF
L9D 9F< 9 N=JLA;9D H9KK &F L@= @GJARGFL9D H9KK AL ;9D;MD9L=K L@= 9N=J9?= G>
L@= N9DM= G> L@= 9;LM9D HAP=D 9F< 9 ;=JL9AF FME:=J G> HAP=DK LG L@= D=>L
9F< LG L@= JA?@L 9F< L@=F AL J=HD9;=K L@= 9;LM9D HAP=DK N9DM= OAL@ L@AK
9N=J9?= 1@= N=JLA;9D H9KK AK L@= K9E= OAL@ L@= <A>>=J=F;= L@9L AFKL=9<
G> MKAF? L@= D=>L 9F< JA?@L F=A?@:GJK G> L@= 9;LM9D HAP=D L@= HAP=DK 9:GN=
9F< :=DGO 9J= MK=< LG ;9D;MD9L= L@= 9N=J9?= 1@= 9N=J9?AF? AK <GF= K=H
9J9L=DQ >GJ 9DD ;GDGJ ;@9FF=DK
1@= FME:=J G> F=A?@:GJAF? HAP=DK AF;DM<=< AF L@= ;9D;MD9LAGF 9N
=J9?AF? OAF<GO AFZM=F;=K L@= 9EGMFL :Q O@A;@ L@= AE9?= OADD :=
:DMJJ=< #GJ <=;J=9KAF? L@= AE9?= <=L9ADK :Q 9 >9;LGJ G>  @9D> G> L@= D=>L
F=A?@:GJ L@= 9;LM9D HAP=D 9F< @9D> G> L@= JA?@L F=A?@:GJ AK MK=< >GJ ;9D
;MD9LAF? L@= 9N=J9?= 9N=J9?AF? OAF<GO   HAP=DK #GJ <=;J=9KAF? L@=
AE9?= <=L9ADK :Q 9 >9;LGJ G>  @9D> G> L@= K=;GF< D=>L F=A?@:GJ L@= D=>L
F=A?@:GJ L@= 9;LM9D HAP=D L@= JA?@L F=A?@:GJ 9F< L@= @9D> G> L@= K=;GF<
JA?@L F=A?@:GJ AK MK=< 9N=J9?AF? OAF<GO   HAP=DK #GJ <=;J=9KAF?
L@= AE9?= <=L9ADK GF= KL=H >MJL@=J GF= EGJ= G> L@= D=>L F=A?@:GJK 9F<
GF= EGJ= G> L@= JA?@L F=A?@:GJK @9N= LG := MK=< >GJ ;9D;MD9LAF? L@= 9N
=J9?= 9N=J9?AF? OAF<GO  <=;J=9K= >9;LGJ \  ×
%GO=N=J L@=J= AK 9 HJG:D=E OAL@ L@AK 9HHJG9;@ DMJJAF? OAL@ GFDQ
GF= 9N=J9?AF? OAF<GO ;9F D=9N= <=L9ADK NAKA:D= L@9L 9J= KE9DD=J L@9F L@=
9N=J9?AF? OAF<GO 1G GN=J;GE= L@AK HJG:D=E L@= :DMJJAF? @9K LG := 9H
HDA=< AF;J=E=FL9DDQ #GJ =P9EHD= O@=F 9AEAF? LG J=<M;= L@= AE9?= <=
L9ADK :Q 9 >9;LGJ G>  YJKL 9 :DMJ OAL@ 9F 9N=J9?AF? OAF<GO G>  HAP=DK
L@=F 9 K=;GF< GF= OAL@ 9F 9N=J9?AF? OAF<GO G>  HAP=DK 9F< YF9DDQ 9
L@AJ< GF= OAL@ 9F 9N=J9?AF? OAF<GO G>  HAP=DK @9K LG := H=J>GJE=< 
<=EGFKLJ9LAGF G> L@= =>>=;L G> <A>>=J=FL 9EGMFLK G> J=<M;LAGF G> AE9?=
<=L9AD ;9F := G:K=JN=< GF #A? 
References
:<9A ' $=J?=DQ  -=LJó " 1GHáD ' *ACDóKA   F AFN=KLA?9LAGF GF KG;A9D J=HJ=
K=FL9LAGFK AF9FAE9L= 9?=FL ;9F EAKD=9< <G?K  9FAK >9EADA9JAK AF 9 >GG< ;@GA;= L9KC
-)G0 ,F=   =
<9;@A & (MO9@9L9 % #MBAL9 (  !G?K J=;9DD L@=AJ GOF=JK >9;= MHGF @=9JAF? L@=
GOF=JK NGA;= FAE G?F  W
MKL 2 %M:=J )  1@= JGD= G> AL=E 9F< ;9L=?GJQKH=;AY; AF>GJE9LAGF AF L@=
<AK;JAEAF9LAGF G> H=GHD= NK FGFH=GHD= AE9?=K :Q HA?=GFK FAE )=9JF =
@9N  W
áDAFL  #9J9?ó 1 *=AC= 6 )=FC=A / *ACDóKA Á -GF?Já;R -  !G FGL ;@GGK=
9K & <G!G?K 9NGA< L@= >GG< L@9L AK AF<A;9L=< :Q 9FGL@=J <G?áK ?9R= AF 9 LOGG:B=;L
;@GA;= L9KC HHD FAE =@9N  W 0;A
9EH:=DD #4 $J==F !$  ,HLA;9D 9F< J=LAF9D >9;LGJK 9>>=;LAF? NAKM9D J=KGDMLAGF
' -@QKAGD )GF<  W
GAD= !  -GDDALR % 0EAL@ '   =@9NAGJ9D <=L=JEAF9LAGF G> ;JALA;9D ZA;C=J >M
KAGF AF <G?K -@QKAGD =@9N  W
GDDA=J9C=J " !9NAK '* 0M<<=F<GJ> 1  !G <G?K  9FAK >9EADA9JAK MF<=JKL9F<
AFNAKA:D= <AKHD9;=E=FL ' GEH -KQ;@GD  W
#AK=L 0 )9F<JQ # ,M=DD=LL= *  "?G;=FLJA; K=9J;@ >GJ <AK9HH=9JAF? G:B=;LK AF <G
E=KLA; <G?K =NA<=F;= >GJ 9 ?=GE=LJA; @QHGL@=KAK G> <AJ=;LAGF FAE G?F  W
$á;KA * *;$J==NQ - (9J9 " *ACDóKA   ">>=;LK G> K=D=;LAGF >GJ ;GGH=J9LAGF 9F<
9LL=FLAGF AF <G?K =@9N J9AF #MF;L  
$9?FGF 0 !GJé #5  0=9J;@ :=@9NAGJ AF N9JAGMK :J==<K G> 9<MDL <G?K  9FAK >9EAD
A9JAK G:B=;L H=JE9F=F;= 9F< GD>9;LGJQ ;M=K ' GEH -KQ;@GD  W
$9RAL & 1=JC=D '  !GEAF9LAGF G> GD>9;LAGF GN=J NAKAGF AF =PHDGKAN=K <=L=;LAGF :Q
<G?K HHD FAE =@9N 0;A  W
$JA=:=D 2 0;@EA<   GDGJ NAKAGF AF L@= 9DA>GJFA9 K=9 DAGF 69DGH@MK ;9DA>GJFA
9FMK 3AK /=K  W
$JA=:=D 2 0;@EA<   JA?@LF=KK <AK;JAEAF9LAGF 9:ADALQ AF L@= 4=KL &F<A9F E9F9
L== 1JA;@=;@MK E9F9LMK ' "PH AGD  W
$JA=:=D 2 0;@EA<   0H=;LJ9D K=FKALANALQ 9F< ;GDGJ NAKAGF AF L@= :GLLD=FGK= <GD
H@AF 1MJKAGHK LJMF;9LMK *9J #J=K@O =@9N -@QKAGD  W
%9J=  1GE9K=DDG *  !GE=KLA; <G?K  9FAK >9EADA9JAK MK= @ME9F 9F< ;GFKH=
;AY; KG;A9D ;M=K LG DG;9L= @A<<=F >GG< ' GEH -KQ;@GD  W
%=?=<üK ! áDAFL  *ACDóKA  -GF?Já;R -  ,OF=JK >9AD LG AFZM=F;= L@= ;@GA;=K
G> <G?K AF 9 LOG;@GA;= NAKM9D HGAFLAF? L9KC =@9NAGMJ  W
UNCORRECTED PROOF
P. Pongrácz et al. Behavioural Processes xxx (2017) xxx-xxx
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>9EADA9JAK 9F< @ME9F AF>9FLK;GEHJ=@=FKAGF G> N9JAGMK >GJEK G> HGAFLAF? ?=KLMJ=K
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G?F  W
*;$J==NQ - $J9KKA 1! %9JE9F *   KLJGF? ;GJJ=D9LAGF =PAKLK :=LO==F
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... This is problematic as little research on the canine visual system is available making it impossible to evaluate whether the visual paradigms used are appropriate for the species. The findings presented in this article highlight that dogs may see the world in a manner quite different from humans, and therefore emphasize the need for such factors to be taken into consideration when evaluating cognition in dogs (Pongrácz, Ujvári, Faragó, Miklósi, & Péter, 2017). By employing species-appropriate methods, in visual perceptual tasks, researchers can more accurately understand how humans' best friends "see" the world. ...
... Examples of some species-appropriate methods include but are not limited to 1) using the dog's primary sensory modality, scent, in addition to using vision; 2) evaluating a dog's ability to discriminate between visual stimuli as a preliminary control, using subject behaviour and not simply software (e.g. DogVision as presented in Pongrácz et al., 2017), before conducting complex assessments that might require assumptions about canine perception 3) considering the ecology and behaviour of dogs when evaluating the suitability of testing paradigms that evaluate visual perception as alterative confounds (e.g. inhibitory control, behavioural flexibility) may affect performance (e.g. ...
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Domestic dogs play many vital roles in human lives; however, relatively little is known about how they perceive the world visually. Given dogs’ recent popularity as a subject in cognitive and behavioural studies, it is important to understand how they visually interpret the world around them. One way to evaluate perception is to assess illusion susceptibility; specifically, how visual information is processed, interpreted and modified post‐retinally. While illusion susceptibility has been used across a variety of species to comparatively assess the similarities and differences in visual processing and perception, this relatively novel methodological approach has only recently been adapted to evaluate perception in domestic dogs. Here, we present a comprehensive overview of the findings from studies that have evaluated domestic dogs’ illusion susceptibility, highlighting the relevance of these results for those studying illusion susceptibility in animals as well as canine behaviour and cognition. More specifically, the ultimate goal of this review is to answer the questions: (a) Are dogs susceptible to visual illusions? (b) If so, are they susceptible to illusions in a way that parallels humans and/or other animals? (c) Are findings, within dogs, consistent and if not, how might these be interpreted and explained?
... In support, in humans, we observed conspecific-preference only in (face-preferring) regions involved in emotional cue processing (Duchaine and Yovel, 2015) but not in (face-preferring) regions involved in structural processing. Additionally, fine-grained, feature-based category selectivity in visual processing may be better developed in species with greater visual acuity, such as primates (Leopold and Rhodes, 2010), but less so in species with poorer visual acuity, such as dogs (Odom et al., 1983;Pongrácz et al., 2017). In the absence of empirical data, it remains an open question whether conspecific-preference is driven by category selectivity or motivational relevance in the dog visual cortex. ...
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Conspecific-preference in social perception is evident for multiple sensory modalities and in many species. There is also a dedicated neural network for face processing in primates. Yet, the evolutionary origin and the relative role of neural species-sensitivity and face-sensitivity in visuo-social processing are largely unknown. In this comparative study, species- and face-sensitivity to identical visual stimuli (videos of human and dog faces and occiputs) were examined using functional magnetic resonance imaging in dogs (n=20; 45% female) and humans (n=30; 50% female). In dogs, the bilateral mid suprasylvian gyrus showed conspecific-preference, no regions exhibited face-preference, and the majority of the visually-responsive cortex showed greater conspecific- than face-preference. In humans, conspecific-preferring regions (the right amygdala/hippocampus and the posterior superior temporal sulcus) also showed face-preference, and much of the visually-responsive cortex showed greater face- than conspecific-preference. Multivariate pattern analyses identified species-sensitive regions in both species, but face-sensitive regions only in humans. Across-species representational similarity analyses revealed stronger correspondence between dog and human response patterns for distinguishing con- from heterospecific faces than other contrasts. Results unveil functional analogies in dog and human visuo-social processing of conspecificity but suggest that cortical specialization for face perception may not be ubiquitous across mammals.
... Some methodological revisions appropriate to the different physiology and evolutionary history of domestic dogs have been made since the field's inception; these revisions use knowledge generated from previous studies-such as an awareness of the importance of the developmental histories, breeds, and training backgrounds of the dogs; and the influence of owner cues on dog behavior (e.g., Miklósi et al. 1998). There is growing awareness that even within the visual modality, the difference between dogs' perception and humans' is important to consider experimentally (Byosiere et al. 2018;Pongrácz et al. 2017). At the same time, given the sensitivity of dogs to odors (e.g., Walker et al. 2006) and significance of olfaction in dogs' perceptual experience (Gadbois and Reeve 2014;Horowitz and Hecht 2014), it is noteworthy that threequarters of studies in canine cognition involve visual tasks (Bensky et al. 2013). ...
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One of the challenges of animal cognition research is overcoming anthropocentric sensory biases—in particular, favoring visual information and cues despite the dominance of other sensory cues in many nonhuman research subjects. As such, it is particularly important for animal cognition researchers to explicitly mention steps taken to control for and attend to the sensory world of their study species. Dogs are well known for their reliance on olfaction, but the extent to which dog cognition and behavior research accounts for olfactory cues or incorporates olfactory controls is unknown. With this bibliographic study, we reviewed canine research published in the past 10 years (2008–2018) in 13 scientific journals and coded the 481 resulting papers for mentions of olfactory or odor cues or controls. Our findings indicate that despite widespread acceptance of the significance of olfaction to dogs, scientific methodology rarely takes olfactory information processing into account. Finally, we propose a simple rubric of recommended reporting of olfactory information in research contexts, with the aims to help attune researchers to the umwelt of their study subjects, and to enhance the methodological reproducibility of canine cognition research.
... First, because these were the colors used in Hamlin et al. (2007). Second, because previous research has shown that dogs can tell them apart (Neitz et al., 1989;Jacobs et al., 1993; see Figure S4 for shapes from a dog's eye view; Pongrácz et al., 2017). Stripes were placed on the target agent in order to align it with the upward angle on the hill and to further differentiate the agent from the helpful and hindering shapes. ...
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Social evaluative abilities emerge in human infancy, highlighting their importance in shaping our species' early understanding of the social world. Remarkably, infants show social evaluation in relatively abstract contexts: for instance, preferring a wooden shape that helps another shape in a puppet show over a shape that hinders another character (Hamlin et al., 2007). Here we ask whether these abstract social evaluative abilities are shared with other species. Domestic dogs provide an ideal animal species in which to address this question because this species cooperates extensively with conspecifics and humans and may thus benefit from a more general ability to socially evaluate prospective partners. We tested dogs on a social evaluation puppet show task originally used with human infants. Subjects watched a helpful shape aid an agent in achieving its goal and a hinderer shape prevent an agent from achieving its goal. We examined (1) whether dogs showed a preference for the helpful or hinderer shape, (2) whether dogs exhibited longer exploration of the helpful or hinderer shape, and (3) whether dogs were more likely to engage with their handlers during the helper or hinderer events. In contrast to human infants, dogs showed no preference for either the helper or the hinderer, nor were they more likely to engage with their handlers during helper or hinderer events. Dogs did spend more time exploring the hindering shape, perhaps indicating that they were puzzled by the agent's unhelpful behavior. However, this preference was moderated by a preference for one of the two shapes, regardless of role. These findings suggest that, relative to infants, dogs show weak or absent social evaluative abilities when presented with abstract events and point to constraints on dogs' abilities to evaluate others' behavior.
... The physical features of the veterinary clinic environment, from the waiting room and treatment area to colours used for furniture or on walls may also influence a dog's experience (Dawson et al., 2016;Overall, 2013). Dogs see differently to humans (Miller and Murphy, 1995;Pongracz et al., 2017), and differences in perception of brightness, colour and acuity should be taken into account for veterinary clinic design. Greater insight into how dogs perceive and experience the veterinary environment will assist in developing strategies to ameliorate stress during veterinary care. ...
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The olfactory sense of the domestic dog is widely recognized as being highly sensitive with a diverse function; however, little is known about the structure of its olfactory system. This study examined a cohort of mixed-sex mesaticephalic canines and used diffusion tensor imaging (DTI), an MRI technique, to map connections from the olfactory bulb to other cortical regions of the brain. The results were validated using the Klingler dissection method. An extensive pathway composed of five white matter tracts connecting to the occipital lobe, cortical spinal tract, limbic system, piriform lobe, and entorhinal pathway was identified. This is the first documentation of a direct connection between the olfactory bulb and occipital lobe in any species and is a step toward further understanding how the dog integrates olfactory stimuli into their cognitive function.SIGNIFICANCE STATEMENT The highly sensitive olfactory system of the domestic dog is largely unexplored. We applied diffusion tractography and dissection techniques to evaluate the white matter connections associated with the olfactory system in a large cohort of dogs. We discovered an extensive white matter network extending from the olfactory bulb to form novel connections directly to other cortices of the brain. This is the first documentation of these novel olfactory connections and provides new insight into how dogs integrate olfactory stimuli in their cognitive functioning.
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The visual system is known to be vital for cognition and perception in the feline and canine and much behavioral research for these species has used visual stimuli and focused on visual perception. There has been extensive investigations into the visual pathway in cats and dogs via histological and neurobiological methods, however to date, only one study has mapped the canine optic pathway in vivo. Advanced imaging methods such as diffusion MRI (DTI) have been routinely used in human research to study the visual system in vivo. This study applied DTI imaging methods to assess and characterize the optic pathway of feline and canine subjects in vivo. The optic nerve (ON), optic tract (OT), and optic radiation (OR) were successfully delineated for each species and the average volume and FA for each tract is reported. The application of DTI to map the optic pathway for canine and feline subjects provides a healthy baseline for comparison in future studies.
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It was shown earlier that dogs, when selecting between two dishes with snacks placed in front of them, left and right, prefer to turn either clockwise or counterclockwise or randomly in either direction. This preference (or non-preference) is individually consistent in all trials but it is biased in favor of north if they choose between dishes positioned north and east or north and west, a phenomenon denoted as “pull of the north”. Here, we replicated these experiments indoors, in magnetic coils, under natural magnetic field and under magnetic field shifted 90° clockwise. We demonstrate that "pull of the north" was present also in an environment without any outdoor cues and that the magnetic (and not topographic) north exerted the effect. The detailed analysis shows that the phenomenon involves also "repulsion of the south". The clockwise turning preference in the right-preferring dogs is more pronounced in the S-W combination, while the counterclockwise turning preference in the left-preferring dogs is pronounced in the S-E combination. In this way, south-placed dishes are less frequently chosen than would be expected, while the north-placed dishes are apparently more preferred. Turning preference did not correlate with the motoric paw laterality (Kong test). Given that the choice of a dish is visually guided, we postulate that the turning preference was determined by the dominant eye, so that a dominant right eye resulted in clockwise, and a dominant left eye in counterclockwise turning. Assuming further that magnetoreception in canines is based on the radical-pair mechanism, a "conflict of interests" may be expected, if the dominant eye guides turning away from north, yet the contralateral eye "sees the north", which generally acts attractive, provoking body alignment along the north-south axis.
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