Dichotic listening for vowel-consonant syllables

This project stands out from my main projects, and aims to explore the generalizability of a popular experimental approach, rather than theoretical development. The design is simple and the paper is short with unsurprising results, although I think it provides necessary clarification to otherwise unanswered questions.

In our lab (and I think also a lot of other labs) we use a number of different variations of the dichotic listening (DL) task, but we tend to use a standard set of stimuli, namely the nonsense syllables constructed by the six stop-consonants followed by the vowel "a", constituting the consonant vowel, or CV syllables: BA / DA / GA / PA / TA / KA. When presenting one of these CV syllables in one ear simultaneously as a different CV syllable in the other ear, participants tend to report the CV syllable presented in the right ear, an effect referred to as the right ear advantage (REA). This effect is explained as left cortical hemisphere having an advantage in language processing and sensory fibres going from each ear to the hemisphere on the opposite side. Studies using DL with CV syllables have been used to explore both attentional effects and clinical groups. However, DL is often used in arguments concerning language in general, although the task only uses a small subset of the language phonemes. In this project, I wanted to test whether the REA could also be found when using different kinds of syllables. I also wanted to see how different types of syllables are selected between when presented simultaneously.

I constructed new stimuli, some with the same CV structure as in earlier experiments, while others used the same consonants and vowels, but in reverse order, i.e. vowel-consonant (VC) syllables. Both types of syllables were paired up in all four left-right combinations: CV-CV, CV-VC, VC-CV and VC-VC. Participants were asked to report which consonant they heard. Results showed that the REA was found both for CV and for VC dichotic pairs, thus showing that that the typical assumptions behind DL can be extended to a wider array of phonemes than just the CV syllables. Further, when CV is presented in one ear and VC in the other, CV has a perceptual advantage. In the paper's discussion, I go through some of the research from the sixties and seventies when different types of stimuli were used in DL, and see to which extent they showed a REA.

The right ear advantage revisited: Speech lateralisation in DL using CV and VC syllables - Laterality

List of open access journals in psychology

I've been looking for a list of open access journals in the field of psychology, and the most complete lists seems to be the one offered by the Directory of Open Access Journals. Unfortunately, the directory has limited search and filter options, and does not have an option for downloading it in spreadsheet format, which would make it easier to manage oneself.

I exported all the entries matching the search term "Psychology" form the directory on October 4th 2012, and painstakingly parsed the results into a spreadsheet format, which allows for filters. The list is online here, and may be useful for others: Spreadsheet list of open access publications in psychology

Selective attention, positive and negative priming in a sequence of dichotic listening trials

In the early years of my Ph.D., I wanted to do an ERP study of my basic primed dichotic listening paradigm. My supervisor Kenneth Hugdahl and my collaborator (and unofficial supervisor) Tom Eichele wanted me to do an ERP study of a standard dichotic listening task first, so we went ahead with that. Participants sat in a comfy chair with electrodes pasted on their scalp and did sequences of dichotic listening trials for 40 minutes. A short beep at the beginning of every trial directed attention to the left, right or both ears, then two different syllables were played at the same time, one in each ear, and the participants were to indicate what they had heard. However, when the results came in, we weren't able to make sense of the results. The EEG results didn't show the lateralized effects we had expected, and the behavioural effects of attending to the instructed side were not as clear as we had expected, so we eventually abandoned the study.

Some years later, after developing my ideas about priming using other behavioural studies, I wanted to test whether I could design a study to show both positive and negative priming effects to interact with instructed attention. I would need a largish dataset in terms of number of participants and trials order to tease out what could be rather weak effects. It then occurred to me that I already had such a dataset sitting on my hard drive, so I picked up the behavioural data from the ERP dataset, and applied analyses to it according to the new theoretical model.

The results section is somewhat complex as it tests for five different hypotheses. Basically this paper reproduces some of the effects shown in previous papers (overall inhibitory selection effects of repetition, negative priming of decreased likelihood to select a recently ignored stimulus, and priming effects interact with instructed attention), as well as showing some novel effects predicted by the model (positive priming effect of increased likelihood to select a recently attended stimulus, interaction between priming and instructed attention is demonstrated in a sequential dichotic listening task). As opposed to what competing theoretical models of priming would have predicted, the selection criteria on the prime trial did not influence the priming effect.

Sætrevik (2012) Facilitating and inhibiting effects of priming and selection criteria in a sequence of DL trials - SJoP

The effect of simultaneous visual stimuli on dichotic listening selection

This study was more or less a side project that does not quite fit in to the rest of my dichotic listening studies. The aim was simply to see if the dichotic listening selection would be influenced by simultaneous ecological visual stimuli. I made brief videos of a mouth pronouncing each of the six syllables, and played one of them simultaneously as the audio for the same syllable was played in one ear, and the audio of another syllable was played in the opposite ear. Participants were asked to report which sound they had heard. Unsurprisingly, the video presentation had the effect of increasing selection of the audio stream that matched the video.

In a way this study was the opposite of my priming studies: Rather than manipulating the selection between two equally valid simultaneous stimuli, the current study made one of the simultaneous stimuli "more valid" by adding a visual channel of information. The effect is reminiscent of the McGurk effect, but in this case it does not create a new percept, it simply "tips the scales" to select one rather than the other.

Sætrevik (2010) The influence of visual information on auditory lateralization - SJoP

Negative priming in a sequence of dichotic listening trials

The previous studies had shown that presenting a single syllable that the participant was supposed to ignore made it less noticeable in an immediately subsequent pair of dichotic syllables. However, the rather artificial experiment situation allowed one to questions of the effect's generalizability. Further, we don't really know what the participant is doing when instructed to "ignore the first sound". According to my theory, the negative priming effect should appear in any situation where a recently ignored stimulus is repeated. As classical theories considered the dichotic listening situation in itself (an information funnel where two bits of information enter and one come out) to be resolved by attenuating one signal but also inhibiting the other signal, it occurred to me that I could simply loop the process, and make one dichotic selection constitute the priming process for the next dichotic selection, which could again prime the next dichotic selection and so on.

Thus, as the dichotic listening paradigm used in our group presents one syllable to be attended and one to be ignored, I could leave behind the somewhat convoluted prime-target task design I had used in my previous studies, and simply present a sequence of dichotic listening trials (without any attention instruction). I adjusted the on-line randomization of stimulus selection to make sure that 50% of the trials repeated one (but not both) of the stimuli presented on the previous trial. In the analysis of the trials with repetitions, I considered every trial n to be the prime for trial n+1. Whether the repeated prime syllable was expected to have a negative or positive effect on n+1, depended on whether the participant selected to attend it or not (for whatever reason) on the prime trial n. E.g., if trial n presents the syllables "Pa" and "Ta" and the participant selects "Pa", then "Ta" was considered to have been inhibited, and if trial n+1 presented "Ta" and "Da", then "Ta" should have a reduced likelihood of being selected. The results did indeed show such a negative priming effect. A converse positive priming effect was indicated, but failed to reach significance (although it was shown in a later study).

The main contributions of this study was (1) to show that sequence effects are apparent in even rather simple dichotic listening tasks without any convoluted priming procedure, and (2) that negative priming effects could be seen in a sequential task with free choices where the prime selection is made arbitrarily. This second point has some relevance for theoretical development, since at least some reading of previous negative priming theories stated that the prime selection would have to be based on a pre-defined selection criteria in order to cause subsequent negative priming effects. I began to formulate what I consider to be a more parsimonious model to account for priming effects, where different nodes in a network achieve different levels of activation based on the stimulus input, but also retains positive or negative activation from preceding selection.

Sætrevik (2010) A biased competition model accounts for negative priming in a free choice situation as residual effects of inhibitory conflict resolution - Neuroscience Letters