Learning from the behaviors and experiences of others

Learning to fear and avoid what is dangerous is crucial for survival. Perhaps equally important is the ability to learn that something which was previously dangerous is now safe. Although we can learn about dangers individually, through our own experiences, it is likely more safe to learn about them from others, by observing their behaviors and reactions. In a sense, this allows us to learn through the experiences of others. The overarching goal of this thesis is to deepen our understanding of how we learn about fear and safety through observation of others. In Study I we let participants undergo an observational extinction paradigm to investigate if safety learning was facilitated through observation of a calm learning model. In a direct conditioning stage participants first learned to associate a stimulus with fear. Next, they learned through that the previously feared stimulus was now safe. This extinction of fear was either direct or vicarious (observational). We demonstrated that attenuation of fear was greater following vicarious rather than direct extinction. We further showed that this was driven by the learning model’s experience of safety. Although learning through others is likely an efficient way of learning, observational learning also has to be applied critically, for instance by not copying the choices of someone that performs poorly. In Study II and Study III we investigated how people learned to make choices through observation of others, demonstrators, which had either a high or low ability. In both studies, participants learned a simple probabilistic two-choice task to avoid shock. Results from Study II demonstrated that people were able to use the observational information to improve performance regardless of the ability (skill) of the demonstrator. They only copied the choices of the demonstrator with high ability and they were able to learn from observing the consequences of a demonstrator’s choice regardless of the demonstrator’s ability. In Study III we also provided participants with descriptions of the abilities of the demonstrators. Our results showed that describing the demonstrator as low in ability impaired observational learning, regardless of the actual ability of the demonstrator and that this is likely driven by a difference in attention directed towards the observational information. An inability to discriminate threatening from safe stimuli is typical for individuals suffering from anxiety. In Study IV we investigated how observational fear conditioning is affected by the learning model’s expressed anticipatory anxiety. Results showed that participants were able to discriminate the threatening from the safe stimuli equally well from a learning model that behaved anxiously (i.e. did not discriminate) as from one that did not behave anxiously (i.e. did discriminate). The results presented in this thesis increase our understanding of how healthy individuals learn about aversive events and stimuli through observation of the behaviors and reactions of others and how these reflect the observed individuals’ experiences

Downflows in sunspot umbral dots

We study the velocity field of umbral dots at a resolution of 0.14". Our analysis is based on full Stokes spectropolarimetric measurements of a pore taken with the CRISP instrument at the Swedish 1-m Solar Telescope. We determine the flow velocity at different heights in the photosphere from a bisector analysis of the Fe I 630 nm lines. In addtion, we use the observed Stokes Q, U, and V profiles to characterize the magnetic properties of these structures. We find that most umbral dots are associated with strong upflows in deep photospheric layers. Some of them also show concentrated patches of downflows at their edges, with sizes of about 0.25", velocities of up to 1000 m/s, and enhanced net circular polarization signals. The downflows evolve rapidly and have lifetimes of only a few minutes. These results appear to validate numerical models of magnetoconvection in the presence of strong magnetic fields.Comment: Final published version. For best quality figures, please download the PS versio

CRISP Spectropolarimetric Imaging of Penumbral Fine Structure

We discuss penumbral fine structure in a small part of a pore, observed with the CRISP imaging spectropolarimeter at the Swedish 1-m Solar Telescope (SST), close to its diffraction limit of 0.16 arcsec. Milne-Eddington inversions applied to these Stokes data reveal large variations of field strength and inclination angle over dark-cored penumbral intrusions and a dark-cored light bridge. The mid-outer part of this penumbra structure shows 0.3 arcsec wide spines, separated by 1.6 arcsec (1200 km) and associated with 30 deg inclination variations. Between these spines, there are no small-scale magnetic structures that easily can be be identified with individual flux tubes. A structure with nearly 10 deg more vertical and weaker magnetic field is seen midways between two spines. This structure is co-spatial with the brightest penumbral filament, possibly indicating the location of a convective upflow from below.Comment: Accepted for publication in ApJL 17 Oct 2008. One Figure adde

Temporal Evolution of Velocity and Magnetic Field in and around Umbral Dots

We study the temporal evolution of umbral dots (UDs) using measurements from the CRISP imaging spectropolarimeter at the Swedish 1-m Solar Telescope. Scans of the magnetically sensitive 630 nm iron lines were performed under stable atmospheric conditions for 71 min with a cadence of 63 s. These observations allow us to investigate the magnetic field and velocity in and around UDs at a resolution approaching 0.13". From the analysis of 339 UDs, we draw the following conclusions: (1)UDs show clear hints of upflows, as predicted by magnetohydrodynamic (MHD) simulations. By contrast, we could not find systematic downflow signals. Only in very deep layers we detect localized downflows around UDs, but they do not persist in time. (2) We confirm that UDs exhibit weaker and more inclined fields than their surroundings, as reported previously. However, UDs that have strong fields above 2000 G or are in the decay phase show enhanced and more vertical fields. (3)There are enhanced fields at the migration front of UDs detached from penumbral grains, as if their motion were impeded by the ambient field. (4) Long-lived UDs travel longer distances with slower proper motions. Our results appear to confirm some aspects of recent numerical simulations of magnetoconvection in the umbra (e.g., the existence of upflows in UDs), but not others (e.g., the systematic weakening of the magnetic field at the position of UDs.)Comment: 27 pages, 26 figures, accepted for publication in the Astrophysical Journa