Hey there,
now I have another problem with selectionmode. I have 3 conditions (resMas, kitsch and nonresMas)  and in each condition I have a different amout of variables. 
Now I want to show all images of each condition just once and they should be selected randomly. I have tried it with /select = noreplace in the picture-Item and sequence in the block element as you can see in the code. I think the pictures are selected randomly BUT the picture of the kitsch and resMas-condition are shown multiple times.

**************************************************************************************************************
**************************************************************************************************************
  Stimulus Items

**************************************************************************************************************
**************************************************************************************************************

<item resonant_masterpieces>
/1 = "Freiheit.jpg"
/2 = "Straße_mit_Zypressen_und_Gestrinen.jpg"
/3 = "nachtcafe-place-lamartine-arles.jpg"
/4 = "Geige_und_Trauben.jpg"
/5 = "Selbstbild_Dürer.jpg"
/6 = "asche.jpg"
/7 = "Der_Wanderer_über_dem_Nebelmeer.jpg"
/8 = "Cliffs_on_Rügen.jpg"
/9 = "Weltgericht.jpg"
/10 = "Vision_nach_der_Predigt.jpg"
/11 = "Adele_Bloch-Bauer.jpg"
/12 = "Selbstbildnis-mit-Judenkirschen.jpg"
/13 = "Auf_der_Schaukel.jpg"
/14 = "Brücke_von_Courbevoie.jpg"
/15 = "Toulouse_A_la_Mie.jpg"
/16 = "Absinth.jpg"
/17 = "Woman-in-the-bathtub.jpg"
/18 = "Le_cheval_blanc.jpg"
/19 = "liebe_und_schmerz.jpg"
/20 = "Vanitassymbole.jpg"
/21 = "die_folgen_des_krieges.jpg"
/22 = "die-verkuendigung.jpg"
/23 = "El_Greco_Laocoon.jpg"
/24 = "Frühstück_der_Ruderer.jpg"
/25 = "Erschaffung_Adam.jpg"
/26 = "Rembrandt_Das_Opfer.jpg"
/27 = "Head_of_Goliath.jpg"
/28 = "die_vier_erdteile.jpg"
/29 = "Cotan_Stilleben.jpg"
/30 = "Noli_me_Tangere.jpg"
</item>

<item nonresonant_masterpieces>
/1 = "C:\Users\Julia\Inquisit_Masterarbeit\Bild1.jpg"
/2 = "C:\Users\Julia\Inquisit_Masterarbeit\Bild2.jpg"
</item>

<item kitsch>
/1 = "C:\Users\Julia\Inquisit_Masterarbeit\kitsch1.jpg"
/2 = "C:\Users\Julia\Inquisit_Masterarbeit\kitsch2.jpg"
</item>

<text fixationCross>
/ items = ("+")
/ fontstyle = ("Arial", 300px)
/ color = (0, 0, 0)
</text>

<picture resMas>
/items = resonant_masterpieces
/select = noreplace
/position = (50%, 50%)
/size = (1620px, 911px)
/select = noreplace
</picture>

<picture nonresMas>
/items = nonresonant_masterpieces
/select = noreplace
/position = (50%, 50%)
/size = (1620px, 911px)
/select = noreplace
</picture>

<picture kitsch>
/items = kitsch
/select = noreplace
/position = (50%, 50%)
/size = (1620px, 911px)
/select = noreplace
</picture>

<radiobuttons ratingquestionLiking>
/ caption="Wie gefällt Ihnen das Kunstwerk?"
/ options=("Sehr gut", "Gut", "Durchschnittlich", "Weniger", "Gar nicht")
/ optionvalues = ("1", "2", "3", "4", "5")
/ required=true
</radiobuttons>

<radiobuttons ratingquestionUnderstanding>
/ caption="Wie gut verstehen Sie das Kunstwerk?"
/ options=("Sehr gut", "Gut", "Durchschnittlich", "Weniger", "Gar nicht")
/ optionvalues = ("1", "2", "3", "4", "5")
/ required=true
</radiobuttons>

<radiobuttons ratingquestionWTP>
/ caption="Wie groß ist Ihre Bereitschaft Geld dafür zu zahlen, dieses Kunstwerk im Museum zu sehen?"
/ options=("Sehr hoch", "Hoch", "Durschnittlich hoch", "Weniger hoch", "Gar nicht hoch")
/ optionvalues = ("1", "2", "3", "4", "5")
/ required=true
</radiobuttons>


**************************************************************************************************************
**************************************************************************************************************
TRIALS
**************************************************************************************************************
**************************************************************************************************************

<trial resMas>
/ stimulustimes = [0=fixationCross; 2000=resMas]
/branch = [surveypage.ratingPage]
/timeout = 10000
/ pretrialpause=3000
</trial>

<trial nonresMas>
/ stimulustimes = [0=fixationCross; 2000=nonresMas]
/branch = [surveypage.ratingPage]
/timeout = 10000
/ pretrialpause=3000
</trial>

<trial kitsch>
/ stimulustimes=[0=fixationCross; 2000=kitsch]
/branch = [surveypage.ratingPage]
/timeout = 10000
/ pretrialpause=3000
</trial>

<surveypage ratingPage>
/caption = "Please answer the following items to the best of your ability"
/questions=[1=ratingquestionLiking; 2=ratingquestionUnderstanding; 3=ratingquestionWTP]
/finishlabel="Weiter"
/caption = "Bitte beantworten Sie folgende Fragen über das zuletzt gezeigte Bild:"
</surveypage>

<block EXP>
/trials = [1-34 = sequence(resMas, nonresMas, kitsch)]
</block>

<expt>
/blocks = [1 = EXP]
</expt>

Can somebody help?

Best regards 

Julia

Thanks for your help! But then the trials are not mixed like on picture from the trial resMas, than one picture form the trial nonresMas and than one ´picture from the trial resMas again....

Thanks for your help! But then the trials are not mixed like on picture from the trial resMas, than one picture form the trial nonresMas and than one ´picture from the trial resMas again....

Just one another question: How can I now store the sequence in which the pictures are shown in a variable. This is important, because I later need to know when which picture was presented and which rating / brain activity belongs to which picture...

You have a full record of the sequence in the data file. You can either use that, or you can set up a <values> entry, concat the current item /ontrialend and log that value to the data file.