Our Amended and Restated 1999 Stock Incentive Plan (the “Plan”) provides for grants of equity-based awards to employees, directors and officers, and advisors (“Eligible Persons”). A maximum of 8,000,000 shares are authorized under the Plan of which 2,450,811 were available for issuance at March 31, 2022. Insiders may participate in plans established pursuant to Rule under the Exchange Act that allow them to exercise awards subject to criteria.

We recognize stock-based compensation expense based on the estimated fair value of awards in accordance with FASB ASC Topic 718 “.” Stock-based compensation expense fluctuates over time as a result of the vesting periods for outstanding awards and the number of awards that actually vest.

The following table reflects the components of stock-based compensation expense recognized in the Condensed Consolidated Statements of Operations for the three-month periods ended March 31, 2022 and 2021:

Eligible employees may receive stock option awards annually with the number of shares and type of instrument generally determined by the employee’s salary grade and performance level. Incentive and stock option awards allow the recipient to purchase shares of our common stock at a set price, not to be less than the closing market price on the date of award, for no consideration payable by the recipient. The related number of shares underlying the stock option is fixed at the time of the grant. Options generally vest over a four-year period with a maximum term of five years from the vesting date. In addition, certain management and professional level employees may receive stock option awards upon the commencement of employment.

one to five years. Restricted stock awards are independent of option grants and are granted at no cost to the recipient other than applicable taxes owed by the recipient. The awards are considered issued and outstanding from the date of grant.

The fair value of each award is estimated as of the date of the grant using the Black-Scholes valuation model. The expected volatility reflects the consideration of the historical volatility of our common stock as determined by the closing price over a six to term commensurate with the expected term of the award. Expected dividends reflect the amount of quarterly distributions authorized and declared on our Class A and Class B common stock as of the grant date. The expected term of the awards is based on evaluations of historical and expected future employee exercise behavior. The risk-free interest rates for periods within the expected term of the award are based on the U.S. Treasury yield curve in effect during the period the options were granted. We have used historical data to estimate future forfeiture rates to apply against the gross amount of compensation expense determined using the valuation model. These estimates have approximated our actual forfeiture rates.

The weighted-average assumptions used to estimate the fair value of the stock options using the Black-Scholes valuation model were as follows for the three-month periods ended March 31, 2022 and 2021:

Activity with respect to the company’s option awards during the three-month period ended March 31, 2022 is as follows:

On March 1, 2022, we issued 8,170

On March 2, 2022, we issued 6,684

Activity with respect to the company’s restricted stock awards during the three-month period ended March 31, 2022 is as follows:

The aggregate intrinsic value represents the difference between the company’s closing stock price on March 31, 2022 of $3.39 and the option exercise price of the shares for stock options that were in the money, multiplied by the number of shares underlying such options. The total fair value of options vested during the periods ended March 31, 2022 and 2021 was $0.2 million and $0.1 million, respectively.

As of March 31, 2022, there was $0.1 million of total unrecognized compensation cost related to stock option awards. This cost is expected to be recognized over a weighted-average period of 3.2 years.