This study considers how inter-individual differences in visual ability are structured. Visual ability could be a single entity (along the lines of general intelligence, or ‘g’), or could be structured according to major anatomical or physiological pathways (dorsal v. ventral streams; magno- v. parvo-cellular systems); or may be a finer-grained mosaic of abilities. To test this, we employed seven visual psychophysical tests (generating 16 measures) on a large (100+) sample of neurotypical participants. A Varimax-rotated PCA (Principal Component Analysis) revealed a two-factor solution that broadly corresponds to a high and low spatial frequency division (consistent with a magno/parvo distinction). Over and above this, two measures (temporal order judgments; gain in contrast sensitivity) correlated with most others, and loaded on both factors, suggesting that they tap broad visual processing demands. These analyses open up further possibilities for exploring the genetic and neuroscientific foundations of differences in visual ability. The tests were also run on a group of individuals with different types of visually-based synaesthesia, given that previous research have suggested they possess a distinct profile of visual abilities. Synaesthesia was linked to enhanced processing of colour and shape/curvature information (amongst others), that may relate to differences in V4 in this group. In conclusion, individual differences in vision are both striking and meaningful, despite our difficulty to imagine seeing the world any differently. This forms part of a larger collection of data considering differences in recognition memory, the diagnosis of sequence-space synaesthesia and the relationship to autism.In this research programme we will investigate enhanced memory in synaesthesia (e.g. experiencing colours for words). Our general approach is to treat synaesthesia as a 'test case' to address other important research questions. For instance, we consider how synaesthesia can inform general theories of memory. Importantly, not all aspects of memory are enhanced in synaesthesia and this can provide insights into how the memory system is structured. Indeed it is not trivially the case that material that elicits 'extra' sensations are better remembered: some material that does not evoke extra sensations (such as abstract figures) are also better remembered by synaesthetes. We suggest that synaesthetes have widespread changes in their perceptual systems (including but not limited to their extra experiences) and that systems supporting perception can also be engaged in memory. We will use both standard and bespoke tests of memory to explore which aspects of memory are enhanced and we will explore how individual differences in perception (in non-synaesthetes) may relate to performance on certain memory tasks.

All tasks were presented on a 39x29 cm CRT monitor with a resolution of 1024 x 768, a refresh rate of 85Hz (screen refresh every 11.8ms) and colour depth of 24 Bit. They sat at a viewing distance of 1.00m, in a blacked-out room, with their head on a chin rest. Tasks were run using MATLAB R2011b and created using the Cogent Toolbox (http://www.vislab.ucl.ac.uk/cogent.php) for MATLAB (The MathWorks, Natick, MA) and Psychtoolbox (Brainard, 1997). The order of the 7 tasks was randomised.