The OVSST was developed for the purpose of this work. It is inspired by the tunnel effect that describes the visual perception when objects are hidden in a tunnel and finally return with different velocities (Burke, 1952; Flombaum & Scholl, 2006)1. The aim of the task was to investigate how people build up a new mental representation of a spatial probability concept over time without prior knowledge to avoid familiarity biases (Ellis, 2012; Starling, 2012). Further, the task should fulfill two requirements: 1) there should be enough capacity in the visual working memory to be sure that the presented stimuli are perceived, 2) stimuli have to be salient to gain attention. Then, allocated information can be processed, stored in long-term memory and retrieved from memory, which are the prerequisites for the development of a mental representation.
In the OVSST the presented stimuli are designed as dark grey (RGB: 128, 128, 128) geometric objects with a diameter of 2 cm. A black square (“room” or “tunnel”) is constantly presented on the screen and is of the dimensions 20x20 cm positioned in the middle of the screen with three exits and a bottom entrance each 2 x 0.5 cm. Participants are instructed to perform two tasks: a prediction and a reaction task. First, participants observe one of three distinct dark gray objects (triangle, square or circle) moving from the bottom entrance into the quadratic room with the three exits (Fig. 2.1). After the object disappeared, participants have to predict as accurately as possible with the arrow keys (left,
1 This concept of tunnel effect has to be distinguished from the tunnel effect which describes limitations in the visual field. The latter meaning is less relevant in the context of the current research paradigm.
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top, right) on the keyboard at which of the exits (left, top, right) these objects will reappear (Instruction: “Versuche so gut wie möglich mit den Pfeiltasten (links, oben, rechts) vorherzusagen an welchem Ausgang das Objekt erscheint”). Participants were asked to put the index finger on the left key, the middle finger on the top key and the ring finger on the right key. Each object was associated with a higher probability of 74 % to one of the exits and with a lower probability of 11% to each of the other two exits (cf. Miller, 1998). In 4% of the trials the object reappeared at the entrance. In order to perform the prediction task as accurate as possible, participants have to learn the probability concept. Finally, the object reappears at one of the exits. The response was designed as a go/no-go task, thus in 50 percent of the trials the object reappeared with a changed color intensity (light gray, RGB: 223, 223, 223). In these trials participants had to press the appropriate arrow key as quickly as possible, for example, the left arrow key if the object reappeared at the left exit. If there was no color change, participants were instructed just to observe the situation (Instruction: “Sobald das Objekt aus einem der Ausgänge wieder austritt, solltest du schnellstmöglich die entsprechende Pfeiltaste drücken, aber nur wenn sich die Farbe des Objekts geändert hat. Ansonsten wartest du ab bis der nächste Durchgang beginnt.”). This task was employed to force participants to process stimulus information and not only the physical emergence of the stimuli. In general, participants had to search visually for information at the three exits in order to receive performance feedback. This feedback is integrated in the mental representation of the participants so that they learn the probability structure of the OVSST and are able to improve the performance.
As mentioned above the OVSST contains another special characteristic: In 4% of the cases, objects reappear at the bottom entrance as a rare occurrence. The aim of this rare occurrence was to analyze how people deal with a special unexpected and uncertain situation. Auditory feedback indicates erroneous task performance in the prediction task, i.e. if the arrow key is pressed too late (“zu schnell”) or too early (“zu langsam”), and in the reaction task if participants respond incorrectly (“falsch reagiert”). At the end of the task, participants are asked to complete a paper-pencil questionnaire concerning the participants’ conscious representation of the probability concept – the Concept Awareness Questionnaire (see Appendix A).
The described procedure of the task was the basic version of the OVSST used in experiment I (see Fig. 2.1 for a schematic description). In further experiments stimuli, probabilities and procedures of the OVSST are manipulated in accordance to the research questions described in the introduction. The motivation for the manipulations is described in detail in the respective chapters. Task uncertainty is caused by the instructions, the probability structure of the OVSST as well as the rare occurrence of the stimuli at the bottom entrance. It includes the objective and manipulable uncertainty created by the task as well as the subjective uncertainty perceived by the participants. Over the course of time
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performing the OVSST, task uncertainty should be more and more dominated by objective uncertainty as the familiarity with the task characteristics increases.
Figure 2.1: Schematic description of one trial of the OVSST: First, participants fixate a fixation cross in the middle of the room that appears for 750 ms. Then, one of the three objects (triangle, square, and circle) appears at the bottom entrance of the room for 1 000 ms and moves into the room. After 1 000 ms the object has disappeared into the room and participants are instructed to predict at which exit the object will reappear with the left, right and upper arrow key of the keyboard within 2 000 ms. Finally, the object reappears at one of the exits. The object moves out of the room to the exit position for 2 000 ms and pauses there 1 000 ms. If the object reappears with a changed color intensity, participants have to press the appropriate arrow key again. In total, a trial lasts 7 750 ms.