Which way is up? Grounded mental representations of space

Processing language is postulated to involve a mental simulation, or re-enactment of perceptual, motor, and introspective states that were acquired experientially (Barsalou, 1999, 2008). One such aspect that is mentally simulated during processing of certain concepts is spatial location. For example, upon processing the word “moon” the prominent spatial location of the concept (e.g. ‘upward’) is mentally simulated. In six eye-tracking experiments, we investigate how mental simulations of spatial location affect processing. We first address a conflict in previous literature whereby processing is shown to be impacted in both a facilitatory and inhibitory way. Two of our experiments showed that mental simulations of spatial association facilitate saccades launched toward compatible locations; however, a third experiment showed an inhibitory effect on saccades launched towards incompatible locations. We investigated these differences with further experiments, which led us to conclude that the nature of the effect (facilitatory or inhibitory) is dependent on the demands of the task and, in fitting with the theory of Grounded Cognition (Barsalou, 2008), that mental simulations impact processing in a dynamic way. Three further experiments explored the nature of verticality – specifically, whether ‘up’ is perceived as away from gravity, or above our head. Using similar eye-tracking methods, and by manipulating the position of participants, we were able to dissociate these two possible standpoints. The results showed that mental simulations of spatial location facilitated saccades to compatible locations, but only when verticality was dissociated from gravity (i.e. ‘up’ was above the participant’s head). We conclude that this is not due to an ‘embodied’ mental simulation, but rather a result of heavily ingrained visuo-motor association between vertical space and eye movements.

Chiroptical spectroscopy of biomolecules using chiral plasmonic nanostructures

This thesis explores the potential of chiral plasmonic nanostructures for the ultrasensitive detection of protein structure. These nanostructures support the generation of fields with enhanced chirality relative to circularly polarised light and are an extremely incisive probe of protein structure. In chapter 4 we introduce a nanopatterned Au film (Templated Plasmonic Substrate, TPS) fabricated using a high through-put injection moulding technique which is a viable alternative to expensive lithographically fabricated nanostructures. The optical and chiroptical properties of TPS nanostructures are found to be highly dependent on the coupling between the electric and magnetic modes of the constituent solid and inverse structures. Significantly, refractive index based measurements of strongly coupled TPSs display a similar sensitivity to protein structure as previous lithographic nanostructures. We subsequently endeavour to improve the sensing properties of TPS nanostructures by developing a high through-put nanoscale chemical functionalisation technique. This process involves a chemical protection/deprotection strategy. The protection step generates a self-assembled monolayer (SAM) of a thermally responsive polymer on the TPS surface which inhibits protein binding. The deprotection step exploits the presence of nanolocalised thermal gradients in the water surrounding the TPS upon irradiation with an 8ns pulsed laser to modify the SAM conformation on surfaces with high net chirality. This allows binding of biomaterial in these regions and subsequently enhances the TPS sensitivity levels. In chapter 6 an alternative method for the detection of protein structure using TPS nanostructures is introduced. This technique relies on mediation of the electric/magnetic coupling in the TPS by the adsorbed protein. This phenomenon is probed through both linear reflectance and nonlinear second harmonic generation (SHG) measurements. Detection of protein structure using this method does not require the presence of fields of enhanced chirality whilst it is also sensitive to a larger array of secondary structure motifs than the measurements in chapters 4 and 5. Finally, a preliminary investigation into the detection of mesoscale biological structure is presented. Sensitivity to the mesoscale helical pitch of insulin amyloid fibrils is displayed through the asymmetry in the circular dichroism (CD) of lithographic gammadions of varying thickness upon adsorption of insulin amyloid fibril spherulites and fragmented fibrils. The proposed model for this sensitivity to the helical pitch relies on the vertical height of the nanostructures relative to this structural property as well as the binding orientation of the fibrils.