281
Chapter twelve: Visual and hydrodynamic flow perception
can be directly measured without the need of extracting the signal from noise (Miersch
et al. 2011). In contrast, noise is considerable when the vibrissae of sea lions detect water
movements. However, the noise signal contains a dominant frequency that is modulated
by a hydrodynamic event. As the dominant frequency was found to correlate with flow
velocity, the sea lion can extract flow velocity from the dominant frequency contained
in the signal measured by the vibrissae (Miersch et al. 2011). Consequently, as already
shown (Gläser et al. 2011), sea lions are able to detect and follow hydrodynamic trails.
However, their performance when encountering trials that have aged might be worse
in comparison to harbor seals due to differences inherent in the two types of hydrodynamic sensors.
12.3 Toolbox
Sensory research of the last decades involving marine mammals has shown that there are
still many discoveries to be made. The basis for these discoveries is in our opinion one
central and important method which is “seeing/observing-perceiving-thinking.” Thus we
would like to encourage everybody to use this central method in order to develop and finally
work on ideas that even seem to be “crazy” at first thought (see e.g., Czech-Damal et al. 2011).
12.3.1 Operant conditioning
Sensory abilities are often analyzed in behavioral experiments for which the experimental
subjects need to learn specific tasks. Here fore, the subjects are trained with the help of
operant conditioning (Skinner 1938). The basis for operant conditioning is that the experimental subject is behaviorally active and that it learns from the consequences its behavior
led to. Thus upon showing a specific behavior, which initially might only happen incidentally, the specific behavior is reinforced whereas others have no consequences or are
negatively reinforced or even punished. Over time, the frequency with which a subject
shows the desired behavior will increase, the animal learns, alters its behavior from the
consequences of its behaviors.
When training mammals such as seals, positive reinforcement is sufficient for successful
learning (Pryor 1984; Ramirez 1999). Positive reinforcement usually consists of a primary
reinforcer, a piece of food, and a secondary reinforcer, such as a whistle. The application of a
secondary reinforcer is essential for the precise timing of the reinforcement which might
be difficult with a primary reinforcer under some conditions, and furthermore bridges
the gap until the primary reinforcer can be delivered. A secondary reinforcer needs to be
established using classical conditioning (Pavlov 1902).
12.3.2 Psychophysics
Sensory abilities of an organism are mainly investigated in psychophysical experiments.
The aim of psychophysics is to link sensation and perception with physical stimuli
(Gescheider 1997). The physical stimuli possess parameters that can/have to be measured
and systematically changed. Thus a good access to physics and measurement techniques
is a prerequisite for a good psychophysicist. The well-controllable and measurable stimuli
allow to assess sensory thresholds that can be determined as absolute thresholds defined as
the smallest amount of stimulus energy necessary to produce a sensation or as difference
threshold defined as the amount of change in a stimulus required to produce a just noticeable difference in sensation (Gescheider 1997).
Chapter twelve: Visual and hydrodynamic flow perception
can be directly measured without the need of extracting the signal from noise (Miersch
et al. 2011). In contrast, noise is considerable when the vibrissae of sea lions detect water
movements. However, the noise signal contains a dominant frequency that is modulated
by a hydrodynamic event. As the dominant frequency was found to correlate with flow
velocity, the sea lion can extract flow velocity from the dominant frequency contained
in the signal measured by the vibrissae (Miersch et al. 2011). Consequently, as already
shown (Gläser et al. 2011), sea lions are able to detect and follow hydrodynamic trails.
However, their performance when encountering trials that have aged might be worse
in comparison to harbor seals due to differences inherent in the two types of hydrodynamic sensors.
12.3 Toolbox
Sensory research of the last decades involving marine mammals has shown that there are
still many discoveries to be made. The basis for these discoveries is in our opinion one
central and important method which is “seeing/observing-perceiving-thinking.” Thus we
would like to encourage everybody to use this central method in order to develop and finally
work on ideas that even seem to be “crazy” at first thought (see e.g., Czech-Damal et al. 2011).
12.3.1 Operant conditioning
Sensory abilities are often analyzed in behavioral experiments for which the experimental
subjects need to learn specific tasks. Here fore, the subjects are trained with the help of
operant conditioning (Skinner 1938). The basis for operant conditioning is that the experimental subject is behaviorally active and that it learns from the consequences its behavior
led to. Thus upon showing a specific behavior, which initially might only happen incidentally, the specific behavior is reinforced whereas others have no consequences or are
negatively reinforced or even punished. Over time, the frequency with which a subject
shows the desired behavior will increase, the animal learns, alters its behavior from the
consequences of its behaviors.
When training mammals such as seals, positive reinforcement is sufficient for successful
learning (Pryor 1984; Ramirez 1999). Positive reinforcement usually consists of a primary
reinforcer, a piece of food, and a secondary reinforcer, such as a whistle. The application of a
secondary reinforcer is essential for the precise timing of the reinforcement which might
be difficult with a primary reinforcer under some conditions, and furthermore bridges
the gap until the primary reinforcer can be delivered. A secondary reinforcer needs to be
established using classical conditioning (Pavlov 1902).
12.3.2 Psychophysics
Sensory abilities of an organism are mainly investigated in psychophysical experiments.
The aim of psychophysics is to link sensation and perception with physical stimuli
(Gescheider 1997). The physical stimuli possess parameters that can/have to be measured
and systematically changed. Thus a good access to physics and measurement techniques
is a prerequisite for a good psychophysicist. The well-controllable and measurable stimuli
allow to assess sensory thresholds that can be determined as absolute thresholds defined as
the smallest amount of stimulus energy necessary to produce a sensation or as difference
threshold defined as the amount of change in a stimulus required to produce a just noticeable difference in sensation (Gescheider 1997).