Evolution of signal form

Visual signals, used for communication both within and between species, vary immensely in the forms that they take. How is it that all this splendour has evolved in nature? Since it is the receiver’s preferences that cause selective pressures on signals, elucidating the mechanism behind the response of the signal receiver is vital to gain a closer understanding of the evolutionary process. In my thesis I have therefore investigated how receivers, represented by chickens, Gallus gallus domesticus, respond to different stimuli displayed on a peck-sensitive computer screen. According to the receiver bias hypothesis, animals and humans often express biases when responding to certain stimuli. These biases develop as by-products of how the recognition mechanism categorises and discriminates between stimuli. Since biases are generated from general stimulus processing mechanisms, they occur irrespective of species and type of signal, and it is often possible to predict the direction and intensity of the biases. One of the results from the experiments in my thesis demonstrates that similar experience in different species may generate similar biases. By giving chickens at least some of the experience of human faces as humans presumably have, the chickens subsequently expressed preferences for the same faces as a group of human subjects. Another kind of experience generated a bias for symmetry. This bias developed in the context of training chickens to recognise two mirror images of an asymmetrical stimulus. Untrained chickens and chickens trained on only one of the mirror images expressed no symmetry preferences. The bias produced by the training regime was for a specific symmetrical stimulus which had a strong resemblance to the familiar asymmetrical exemplar, rather than a general preference for symmetry. A further kind of experience, training chickens to respond to some stimuli but not to others, generated a receiver bias for exaggerated stimuli, whereas chickens trained on reversed stimuli developed a bias for less exaggerated stimuli. To investigate the potential of this bias to drive the evolution of signals towards exaggerated forms, a simplified evolutionary process was mimicked. The stimuli variants rejected by the chickens were eliminated, whereas the selected forms were kept and evolved prior to the subsequent display. As a result, signals evolved into exaggerated forms in all tested stimulus dimensions: length, intensity and area, despite the inclusion of a cost to the sender for using increasingly exaggerated signals. The bias was especially strong and persistent for stimuli varying along the intensity dimension where it remained despite extensive training. All the results in my thesis may be predicted by the receiver bias hypothesis. This implies that biases, developed due to stimuli experience, may be significant mechanisms driving the evolution of signal form.

The effects of video games on the receptive vocabulary proficiency of Swedish ESL students

Playing video games is an activity that takes up an increasing amount of children’s and adolescent’s spare time. While some previous studies have highlighted the negative aspects of video games, little research has been carried out on the linguistic learning opportunities that video games present. This study primarily investigates if Swedish second language learners of English can increase their vocabulary proficiency in English with the use of video games. In order to answer the research questions, two quantitative data elicitation methods are used: a questionnaire which aims to gather attitudinal and behavioral data, and a Vocabulary Levels Test which elicits data about the participants’ receptive vocabulary proficiency. The participants consist of 25 students at an upper secondary school in Stockholm. The results show that participants who played video games scored higher on the Vocabulary Levels Test, indicating a higher receptive vocabulary proficiency. Furthermore, the results show that participants who played moderate to frequent amounts of time performed better in the Vocabulary Levels Test than infrequent players. The results also show that video games emphasizing co-operation and communication are preferable to use for vocabulary acquisition. Additionally, the study discusses if video games could be integrated into the Swedish upper secondary school system.