In the dog days of summer, top Wednesday shows “Big Brother” on CBS and “America’s Got Talent” on NBC were both down in young adults from last week, but new dramas “Extant” and “Taxi Brooklyn” held steady, as did CW’s reality series “Penn & Teller: Fool Us.”

According to preliminary national estimates from Nielsen, “Big Brother” was the top show of the night in adults 18-49 (2.0 rating/8 share); it was down 10% in the demo from last week but it should pick up at least a tenth in the nationals. In total viewers, “Brother” was up slightly from last week, and in the nationals it potentially could top the show’s season premiere (6.71 million) as its most-watched Wednesday installment of the season.

CBS followed “Big Brother” with a repeat “Criminal Minds” (0.9/3 in 18-49, 4.9 million viewers overall) and firstrun drama “Extant” (1.0/3 in 18-49, 5.6 million viewers overall). The Halle Berry sci-fi show matched its 18-49 low set last week, beating the original dramas on NBC and ABC in the 10 o’clock hour and standing as the night’s most-watched scripted program overall.

At NBC, an “America’s Got Talent” encore at 8 (1.1/4 in 18-49, 5.8 million viewers overall) was followed by the program’s results show (1.8/6 in 18-49, 9.7 million viewers overall), which was down 10% from last week but likely will add a tenth in the nationals; it was the night’s top show in total viewers. And at 10 p.m., “Taxi Brooklyn” (0.9/3 in 18-49, 5.2 million viewers overall) appears to have matched its score of last week.

NBC tied with CBS and Univision for the night’s lead in adults 18-49 rating while pulling ahead in both 25-54 and total viewers.

Elsewhere, ABC aired repeats of comedies “The Middle” (1.1/4 in 18-49, 4.2 million viewers overall), “The Goldbergs” (1.1/4 in 18-49, 3.7 million viewers overall) and “Modern Family” at both 9 (1.2/4 in 18-49, 3.7 million viewers overall) and 9:30 (1.3/4 in 18-49, 3.9 million viewers overall). It capped the night with firstrun drama “Motive” (0.7/2 in 18-49, 3.5 million viewers overall), which matched the score of its most recent episode.

The ABC repeat comedy block beat out Fox’s fading “So You Think You Can Dance” (1.0/3 in 18-49, 3.4 million viewers overall), which was down a tick to match its low.

At CW, “Penn & Teller: Fool Us” (0.5/2 in 18-49, 1.7 million viewers overall) continues to look good; the magic competition series has delivered the same demo rating for all three of its airings to date, and it rose a bit from last week in total viewers.

Preliminary 18-49 averages for the night: CBS and Univision, 1.3/5; NBC, 1.3/4; ABC and Fox, 1.0/3; Telemundo, 0.7/2; CW, 0.4/1.

In total viewers: NBC, 6.9 million; CBS, 5.7 million; ABC, 3.8 million; Fox and Univision, 3.4 million; Telemundo, 1.6 million; CW, 1.2 million.