Numerical distance effects in visual search

• Applicant: Professor Dr. Wolfgang Schwarz
• Subject Area: General, Cognitive and Mathematical Psychology
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263051666

How does numerical information influence human information processing in elementary perceptual and cognitive tasks? To address this general question, we carried out several eye movement and reaction time experiments; these studies have led to two publications in relevant international journals (JEP:LMC, AP&P).We formulated, and fitted to extensive new data sets, a parsimonious chronometric model which describes and explains in considerable quantitative detail many well-established and several new aspects related to numerical comparison processes (Reike & Schwarz, 2016). We also described a new oculomotor effect (the saccadic overshoot effect): the amplitude of the response saccade increases as the numerical distance of the two digits presented decreases; this effect is well accounted for by the model that we proposed. Previous findings present a rather mixed picture regarding motor aspects of the response behavior in number-related tasks, and the dependency of these aspects on numerical distance. In two planned experiments we intend to investigate in detail the validity and limits of the saccadic overshoot effect. Specifically, we plan to manipulate the number of the digits presented (one vs. two) and also their spatial position within the display (horizontally vs. vertically aligned). Number comparison studies typically focus on properties of the stimuli (i.e., digits) which are unrelated to the events which have taken place in the preceding trial. Also, many of these studies employ stimuli with attributes (e.g., numerical vs. physical size) which potentially induce a representational or response conflict. Using several well-understood conflict paradigms (Snarc, Simon), we have developed a new design within which we demonstrated the systematic effect of manipulating the local trial-to-trial probability of repeating the (response-)irrelevant stimulus attribute, contrasting trials in which the irrelevant attribute is alternated vs. repeated (Schwarz & Reike, 2016). Are these effects specific for, and thus limit to, conflict paradigms, or do they hold more generally? In two new experiments, we intend to address this question, using paradigms in which the relevant and the irrelevant stimulus attribute are unlikely to induce representational or response conflicts. To this end, our participants will judge digits with respect to their physical size, or (in different conditions) their color. In addition, to minimize potential response conflicts we plan to collect not only manual but also vocal choice responses. During the first phase of our project we have developed the software needed to control all aspects of our planned experiments, including the registration and preprocessing of eye movements. Similarly, nearly all programs needed to aggregate and to analyze the data we plan to collect are readily utilizable.

• DFG Programme: Research Grants