Cognitive Abilities in Malawi Cichlids (Pseudotropheus sp.): Matching-to-Sample and Image/Mirror-Image Discriminations

Abstract

The ability to recognize and distinguish between visual stimuli is fundamental for everyday survival of many species. While diverse aspects of cognition, including complex visual discrimination tasks were previously successfully assessed in fish, it remains unknown if fish can learn a matching-to-sample concept using geometrical shapes and discriminate between images and their mirror-image counterparts. For this purpose a total of nine Malawi cichlids (Pseudotropheus sp.) were trained in two matching-to-sample (MTS) and three two-choice discrimination tasks using geometrical, two-dimensional visual stimuli. Two out of the three discrimination experiments focused on the ability to discriminate between images and their mirror-images, the last was a general discrimination test. All fish showed quick associative learning but were unable to perform successfully in a simultaneous MTS procedure within a period of 40 sessions. Three out of eight fish learned to distinguish between an image and its mirror-image when reflected vertically; however none of the fish mastered the task when the stimulus was reflected horizontally. These results suggest a better discrimination ability of vertical compared to horizontal mirror-images, an observation that is widespread in literature on mirror-image discrimination in animals. All fish performed well in the general visual discrimination task, thereby supporting previous results obtained for this species.

Visual Discrimination of Geometric and Complex 2D Shapes in Goldfish (Carassius auratus)

“…While we did not observe any side biases in using the 'correction method' in Experiment 1a or the 'non-correction method' in Experiment 2, we did observe a side bias using the 'correction method' in Experiment 1b. Side biases have been found in other visual discrimination studies with fish (e.g., Colwill, Raymond, Ferreira, & Escudero, 2005;Gierszewski et al, 2013;Graeber & Ebbesson, 1972;Schluessel & Bleckmann, 2005;Schluessel et al, 2014). It would be useful to replicate the current study with more subjects in each experiment so that the two methods can be directly compared, as we are not aware of any studies that have done so using the same species and the same stimuli (Siebeck et al (2009) used both methods, but with different pairs of stimuli).…”

“…In both methods, the fish were reinforced only after a correct choice, and across a set of two sessions the S+ was viewed equally often on the right and left. The 'non-correction' method is more efficient in that data can be collected quicker, but the disadvantage is that sometimes fish will develop a side bias (Gierszewski et al, 2013;Schluessel et al, 2014).…”

“…We should use caution in interpreting results from few subjects because within-species differences between fish can occur (Gierszewski et al, 2013;Lucon-Xiccato, Dadda, & Bisazza, 2016;Miletto Petrazzini & Agrillo, 2016;Schluessel et al, 2012Schluessel et al, , 2015Siebeck et al, 2009;Wyzisk & Neumeyer, 2007). However, other studies have utilized two to five goldfish per experiment or test (Douglas, Eva, & Guttridge, 1988;Freche et al, 2012;Neumeyer, 1992Neumeyer, , 2003Wyzisk & Neumeyer, 2007).…”

“…Previous research showed that learning success for fish engaged in similar visual object discrimination tasks occurred within 350-400 trials (Gierszewski, Bleckmann, & Schluessel, 2013;Schluessel et al, 2012;Sovrano & Bisazza, 2009). Thus, we presented the fish with 77 sessions (385 total trials) for each stimulus pair to ensure there would be an adequate number of trials to learn the discrimination.…”

“…Studies on visual perception in fish have employed both the 'correction method' (e.g., Frech, Vogtsberger, & Neumeyer, 2012;Mackintosh & Sutherland, 1963;Neumeyer, 1992Neumeyer, , 2003Wyzisk & Neumeyer,2007) and the 'non-correction method' (e.g., Gierszewski et al, 2013;Schluessel et al, 2012Schluessel et al, , 2014Siebeck et al, 2009;Sovrano & Bisazza, 2008). In Experiment 1, the 'correction method' was used, meaning that the fish could tap the S-as many times as necessary until they tapped the S+ and received a food reward to end the trial.…”