The effects of payoff manipulations on temporal bisection performance Başak Akdoğan, Fuat Balcı ⁎ Department of Psychology, Koç University, Rumelifeneri Yolu, Sarıyer 34450, Istanbul, Turkey abstract article info Article history: Received 10 December 2015 Received in revised form 6 June 2016 Accepted 15 June 2016 Available online 2 July 2016 There is growing evidence that alterations in reward rates modify timing behavior demonstrating the role of mo- tivational factors in interval timing behavior. This study aimed to investigate the effects of manipulations of re- wards and penalties on temporal bisection performance in humans. Participants were trained to classify experienced time intervals as short or long based on the reference durations. Two groups of participants were tested under three different bias conditions in which either the relative reward magnitude or penalty associated with correct or incorrect categorizations of short and long reference durations was manipulated. Participants adapted their choice behavior (i.e., psychometric functions shifted) based on these payoff manipulations in direc- tions predicted by reward maximization. The signal detection theory-based analysis of the data revealed that payoff contingencies affected the response bias parameter (B″) without altering participants' sensitivity (A′) to temporal distances. Finally, the response time (RT) analysis showed that short categorization RTs increased, whereas long categorization RTs decreased as a function of stimulus durations. However, overall RTs did not ex- hibit any modulation in response to payoff manipulations. Taken together, this study provides additional support for the effects of motivational variables on temporal decision-making. © 2016 Elsevier B.V. All rights reserved. Keywords: Interval timing Motivation Optimality Temporal bisection 1. Introduction Organisms are equipped with a mechanism that enables the timing of intervals across timescales of seconds and minutes, which is denoted as interval timing (Buhusi & Meck, 2005). Research on interval timing suggests that the characteristics of timed response patterns are sensitive to experimental manipulations that presumably affect the motivational states of subjects (e.g., Balcı, 2014; Galtress, Marshall, & Kirkpatrick, 2012). For instance, changes in payoff structures can yield facilitatory ef- fects on timing behavior (Avlar et al., 2015; Çavdaroğlu, Zeki, & Balcı, 2014), expected reward magnitude can modulate the time to initiate anticipatory responding as evidenced by shifts in the timed response curves (e.g., Galtress & Kirkpatrick, 2009; Ludvig, Balcı, & Spetch, 2011; Ludvig, Conover, & Shizgal, 2007), or pre-feeding might lead to the flattening of timed response curves (Ward & Odum, 2007). Howev- er, since previous research investigating motivational factors on timing performance was mostly carried out with nonhuman animals (also see Bizo & White, 1994, 1995; Grace & Nevin, 2000; Guilhardi, MacInnis, Church, & Machado, 2007), how the same factors (e.g., payoff) affect human timing performance remains relatively unclear (but see Balcı, Freestone, & Gallistel, 2009; Balcı, Wiener, Çavdaroğlu, & Coslett, 2013; Çavdaroğlu et al., 2014; Wearden & Grindrod, 2003). This study aims to fill this gap by investigating the changes in temporal discrimina- tion performance of humans as a function of either the reward or penal- ty attributed differentially to correct and incorrect categorizations of durations. A common procedure for studying interval timing performance is the temporal bisection task (e.g., Church & Deluty, 1977). This method requires the classification of a set of time intervals as short and long based on their subjective temporal similarity to previously acquired ref- erence durations. Temporal categorizations in this task rely on both ret- rospective and prospective decision dynamics (Balcı & Simen, 2014), and yield a variety of measures including choice proportions, the impre- cision characteristics of temporal judgments as well as the response times associated with different temporal judgments (a relatively more recently appreciated behavioral endpoint of temporal bisection). Given the advantages of this versatile method, the present study aimed to address the empirical gap that relates to the lack of studies in- vestigating payoff effects on temporal bisection performance of humans. In addition, as recent research conducted with nonhuman an- imals produced evident but inconsistent biasing effects of reward mag- nitude on the shifts in choices and noise characteristics of timed responses in the temporal bisection task (e.g., Avlar et al., 2015; Galtress & Kirkpatrick, 2010), we were further motivated to delineate the adjustments in temporal choice behavior under asymmetrical pay- off matrices. Despite discrepancies in the reported outcomes of reward manipula- tions in the temporal bisection procedure, motivation-mediated Acta Psychologica 170 (2016) 74–83 ⁎ Corresponding author. E-mail addresses: bakdogan@ku.edu.tr (B. Akdoğan), fbalci@ku.edu.tr (F. Balcı). http://dx.doi.org/10.1016/j.actpsy.2016.06.007 0001-6918/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Acta Psychologica journal homepage: www.elsevier.com/locate/actpsy