Receptive field profiles of simple cells in the visual cortex often resemble even-symmetric or odd-symmetric Gabor filters; i.e., their receptive field profiles can be described by the product of a Gaussian and either a cosine or sine function. Their spatial frequency tuning is of medium bandwidth (~ one octave) which is narrow enough for a cell to distinguish the third harmonic from the fundamental frequency for square-wave gratings of low spatial frequency. The responses of adjacent simple cells, tuned to the same spatial frequency, orientation, and direction, differ in their phase response to drifting sine-wave gratings by approxi mately either 90 ° or 180 °. This latter result makes it possible to consider two adjacent simple cell pairs as operating like paired Gaussian-attenuated sine and cosine filters or Gabor filters for restricted regions of visual space. The entire set of simple cells provides a complete representation of the visual scene, yet each simple cell is unique in its response properties. At the complex cell stage, the cell's mean firing rate appears to represent the amplitude of a local Fourier coefficient, but phase information is seldom conveyed with much precision in the action potential code. The relationship of these and other properties of striate neurons to current issues in spatial pattern recognition is discussed. I.

Adjacent simple cells recorded and "isolated" simultaneously from the same microelectrode placement were usually tuned to the same orientation and spatial frequency. The responses of the members of these "spatial frequency pairs" to drifting sine-wave gratings were cross-correlates. Within the middle range of the spatial frequency selectivity curves, the responses of the paired cells differed in phase by approximately 90 percent. This phase relationship suggests that adjacent simple cells tuned to the same spatial frequency and orientation represent paired sine and cosine filters in terms of their processing of afferent spatial inputs and truncated sine and cosine filters in terms of the output of simple cells.

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The surgical results in 78 recent cases of total removal of unilateral acoustic neuroma in which an attempt was made to preserve cochlear function have been added to the authors' previous series of 66 cases to evaluate the factors influencing the ability to preserve useful hearing. Useful hearing was defined by speech reception threshold no poorer than 70 dB and a discrimination score of at least 15%. Analysis using a logistic regression model showed that certain preoperative clinical parameters such as tumor size, speech discrimination score, and gender were significantly correlated with hearing outcome. Favorable outcome was significantly correlated with smaller tumor size, higher preoperative speech discrimination score, and male sex. From this data, an explicit formula was devised for predicting hearing outcome for an individual patient. In four cases with useful hearing preserved, there was improvement of greater than 15 percentage points in speech discrimination scores. While preoperative auditory brainstem responses were not predictive of hearing preservation, monitoring of intraoperative auditory evoked potentials was predictive of hearing outcome in selected cases. Specifically, when wave V was unchanged at the end of the operation, even if it may have been transiently lost during surgery, useful hearing was invariably preserved.