Probing the Perceptual Functions of the Human Lateral Geniculate Nucleus and Primary Visual Cortex with Signal-Detection Theory: An fMRI Study

As the roles of the thalamic nuclei have become better understood, the traditional view of the human lateral geniculate nucleus as a mere relay station has been expanded. For example, robust effects of attentional modulation have been found in the LGN. Such effects have also been found in the primary visual cortex. Capitalizing on this, we used signal-detection theory to further our understanding into their relationship. In our study, subjects identify the presence of a low-contrast grating on a noise annulus pattern in a slow event-related fMRI paradigm (see Ress & Heeger, 2000). BOLD responses were analyzed with a receiver-operator-characteristic (ROC) area under the curve (AUC) approach (e.g. Pessoa & Padmala, 2005), separating the target present/absent (or bottom-up) and response yes/no (top-down) regions. Preliminary results have identified adjacent and partially overlapping voxels of V1 and LGN that discriminate between bottom-up and top-down processing. Furthermore, other areas, like the posterior parietal and frontal cortices, were found to be similarly discriminative. Time-shifted correlation analysis between V1 and LGN is also underway. Our results further elaborate the role of the LGN and extend its involvement in perceptual decisions.