| 1. |
- Tirado Aldana, Carlos, 1991-
(författare)
-
The psychophysics of human echolocation
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Echolocation is the capacity to detect, localize, discriminate, and, overall, gather spatial information from sound reflections. Since we began studying it in humans, we have learned several things. First, most humans can echolocate to some degree. Second, the capacity to echolocate is related to: the type and size of the object that the individual is trying to echolocate; how well the individual can use self-generated or artificial signals; and the distance to the object. Third, the blind tend to perform better than the sighted, although some sighted individuals can perform as well as the blind. It has been speculated that expert echolocators are capable of unlearning the precedence effect (PE), which is the tendency of our auditory system to prioritize spatial information coming from the first wave front instead of the spatial information from the second wave front. This would allow them to obtain more spatial information from echoes, but there is little research linking the PE to echolocation skills, which is why my thesis research has explored this matter. Another contribution of my thesis research was to introduce two new concepts: echo-detection and echo-localization. Echo-detection is the ability to detect an object using echoes as the main cue (“Is the object there, yes or no?”), whereas echo-localization is the ability both to detect and also localize an object using echoes as the main cue (“Is the object situated to the right or left?”). The reason for dividing echolocation into these two tasks is that detecting an echo does not necessarily entail knowing its location. No previous study has compared these two distinct abilities. Echo-detection and echo-localization, though linked to each other, could be influenced by different mechanisms. The aim of this thesis was to explore individual differences in echo-detection, echo-localization, and other fundamental psychoacoustic abilities (i.e., PE and different types of masking) in inexperienced, sighted individuals. This included using a novel tool to train and assess echolocation skills: the Echobot. The Echobot is a machine that automates stimulus presentation. It allows an aluminum disk to be moved to different distances and different echolocation signals to be tested simultaneously. Its main advantage consists of facilitating the use of rigorous psychophysical methods that would otherwise take a long time to perform correctly. Studies I and II focused on individual differences in fundamental hearing abilities that are prerequisites for echo-detection and echo-localization (i.e., PE components and different types of masking). Studies III and IV focused on using the Echobot to study individual performance differences in echo-detection and echo-localization tasks. Overall, the results indicate that echolocation was possible for most participants, regardless of the method or signal used. There were substantial individual differences, and a performance gap between echo-detection and echo-localization appeared in several individuals. Echo-localization was usually more difficult than echo-detection, since spatial information was the hardest to retrieve from the localization tasks. It was possible to close the task performance gap in some individuals through training, but only for time intervals between direct and reflected sound of >20 ms, for which the PE might not operate. Hence, the possibility of “unlearning” the PE to improve echolocation skills remains speculative. Finally, the Echobot proved useful for studying echolocation. Taken together, these results suggest that independent mechanisms make the localization of spatial information more difficult than pure detection. However, in long-inter-click-interval (ICI) conditions, the neural mechanisms are likely mediated by attention and cognitive processes, which are more plastic, and participants can learn to obtain echo-localization information as effectively as echo-detection information. In short-ICI conditions, neural mechanisms seem more related to peripheral and temporal processing, which are potentially less plastic. Further research into individual differences in temporal processing, using brain-imaging techniques such as EEG, might help us understand the different mechanisms influencing echo-detection and echo-localization.
|
|
| 2. |
- Tirado, Carlos, et al.
(författare)
-
Comparing Echo-Detection and Echo-Localization in Sighted Individuals
- 2021
-
Ingår i: Perception. - : SAGE Publications. - 0301-0066 .- 1468-4233. ; 50:4, s. 308-327
-
Tidskriftsartikel (refereegranskat)abstract
- Echolocation is the ability to gather information from sound reflections. Most previous studies have focused on the ability to detect sound reflections, others on the ability to localize sound reflections, but no previous study has compared the two abilities in the same individuals. Our study compared echo-detection (reflecting object present or not?) and echo-localization (reflecting object to the left or right?) in 10 inexperienced sighted participants across 10 distances (1-4.25 m) to the reflecting object, using an automated system for studying human echolocation. There were substantial individual differences, particularly in the performance on the echo-localization task. However, most participants performed better on the detection than the localization task, in particular at the closest distances (1 and 1.7 m), illustrating that it sometimes may be hard to perceive whether an audible reflection came from the left or right.
|
|
| 3. |
- Tirado, Carlos, et al.
(författare)
-
Individual differences in the ability to access spatial information in lag-clicks
- 2021
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 149:5, s. 2963-2975
-
Tidskriftsartikel (refereegranskat)abstract
- It may be difficult to determine whether a dichotic lag-click points to the left or right when preceded by a diotic lead-click. Previous research suggests that this loss of spatial information is most prominent at inter-click intervals (ICIs) <10 ms. However, a study by Nilsson, Tirado, and Szychowska [(2019). J. Acoust. Soc. Am. 145, 512–524] found support for loss of spatial information in lag-clicks at much longer ICIs using a stimulus setup differing from those in previous research. The present study used a setup similar to that of the Nilsson, Tirado, and Szychowska study [(2019). J. Acoust. Soc. Am. 145, 512–524] to measure 13 listeners' ability to lateralize (left versus right) and detect (present versus absent) the lag-click in lead–lag click pairs with ICIs of 6–48 ms. The main finding was distinct individual differences in performance. Some listeners could lateralize lag-clicks all the way down to their detection threshold, whereas others had lateralization thresholds substantially higher than their detection thresholds, i.e., they could not lateralize lag-clicks that they could easily detect. Two such listeners trained for 30 days and managed to improve their lateralization thresholds to reach their detection thresholds, but only at longer ICIs (>20 ms), suggesting different mechanisms underlying lag-click lateralization at short versus long ICIs.
|
|
