Drifting sinusoidal gratings, moving bars, and moving spots were employed to study the direction sensitivity of 425 neurons in the A laminae of the cat's LGNd. Thirty-two percent of X- and Y-type LGNd relay cells exhibit significant direction sensitivity when tested with drifting sinusoidal gratings. X and Y cells exhibit the same degree of direction sensitivity. Moving spots and bars elicit direction specific responses from LGNd cells that are consistent with those elicited when drifting sinusoidal gratings are employed. For cells that are both orientation and direction sensitive, the preferred direction tends to be orthogonal to the preferred orientation. In general, direction sensitivity is strongest at relatively low spatial frequencies, well below the spatial-frequency cutoff for the cell. The presence of significant numbers of direction-sensitive LGNd cells raises the possibility that subcortical direction specificity is important for the generation of this property in the visual cortex.
