On June 30, 2020, the Company issued 1,718 shares of common stock for debt conversion of $1,000 aggregate principal amount of the 8% Notes, related shares of Series C Preferred Stock and 10% Note. The Company also issued 93 shares of common stock for Series C Preferred Stock discussed above (Note 9).

During nine-month period ended June 30, 2019, the Company issued 250 shares of common stock for the conversion of approximately 250 shares of Series B Convertible Preferred Stock, respectively (See Note 11).

Restricted Stock

The Company granted 150 restricted shares of common stock during nine-month period ended June 30, 2020. The restricted shares are to be earned over a three-year period and cliff vest at the end of the third year from the date of grant. The Company did not grant restricted stock during nine-month period ended June 30, 2019. Stock-based compensation expense attributable to restricted stock was $130 and $1,015, and $203 and $608 during the three and nine-month periods ended June 30, 2020 and 2019, respectively. As of June 30, 2020, there was approximately $650 of unrecognized compensation expense related to restricted stock outstanding. On November 23, 2019, 500 shares of restricted common stock held by the Company’s former president became fully vested upon his passing. These shares were issued during nine-month period ended June 30, 2020. No shares were issued during the nine-month period ended June 30, 2019.

Warrants

No warrants were granted or exercised during the nine-month period ended June 30, 2020.

Stock Options

As of June 30, 2020, there were stock options outstanding under the Company’s Second Amended and Restated 1997 Stock Option Plan and the Company’s Amended and Restated 2013 Incentive Stock Plan. Both plans were approved by the shareholders. The plans granted specified numbers of options to non-employee directors, and they authorized the Compensation Committee of the Board of Directors to grant either incentive or non-statutory stock options to employees. Vesting periods are established by the Compensation Committee at the time of grant. All stock options outstanding as of June 30, 2020 and September 30, 2019 were non-statutory stock options, had exercise prices equal to the market price on the date of grant, and had expiration dates ten years from the date of grant.

Stock-based compensation expense attributable to stock options and warrants was $207 and $274 for the three and nine-month periods ended June 30, 2020, and $329 and $1,054 for the three and nine-month periods ended June 30, 2019, respectively. As of June 30, 2020, there was approximately $787 of unrecognized compensation expense related to unvested stock options outstanding, and the weighted average vesting period for those options was 3.96 years.

 A summary of stock option activity is as follows: